diff --git a/TaxBaik.Domain/Entities/Client.cs b/TaxBaik.Domain/Entities/Client.cs
index 85c86d6..00f4f7b 100644
--- a/TaxBaik.Domain/Entities/Client.cs
+++ b/TaxBaik.Domain/Entities/Client.cs
@@ -3,15 +3,28 @@ namespace TaxBaik.Domain.Entities;
 public class Client
 {
     public int Id { get; set; }
-    public string Name { get; set; } = null!;
+    public int? CompanyId { get; set; }
+    public string Name { get; set; } = "";
     public string? CompanyName { get; set; }
     public string? Phone { get; set; }
     public string? Email { get; set; }
+    public string? ContactPerson { get; set; }
     public string? ServiceType { get; set; }
     public string? TaxType { get; set; }
     public string Status { get; set; } = "active";
     public string? Source { get; set; }
     public string? Memo { get; set; }
+
+    // Tax-specific fields
+    public string? BusinessRegistrationNumber { get; set; }
+    public string? BusinessType { get; set; }
+    public DateTime? EstablishmentDate { get; set; }
+    public string? AnnualRevenueRange { get; set; }
+    public int? EmployeeCount { get; set; }
+    public DateTime? LastTaxFilingDate { get; set; }
+    public string TaxRiskLevel { get; set; } = "normal";
+    public DateTime? NextFilingDueDate { get; set; }
+
     public DateTime CreatedAt { get; set; }
     public DateTime UpdatedAt { get; set; }
 }
diff --git a/TaxBaik.Domain/Entities/ConsultingActivity.cs b/TaxBaik.Domain/Entities/ConsultingActivity.cs
new file mode 100644
index 0000000..4ccb793
--- /dev/null
+++ b/TaxBaik.Domain/Entities/ConsultingActivity.cs
@@ -0,0 +1,17 @@
+namespace TaxBaik.Domain.Entities;
+
+public class ConsultingActivity
+{
+    public int Id { get; set; }
+    public int ClientId { get; set; }
+    public string ActivityType { get; set; } = "";
+    public DateTime ActivityDate { get; set; }
+    public TimeOnly? ActivityTime { get; set; }
+    public int? AssignedConsultantId { get; set; }
+    public string Description { get; set; } = "";
+    public string? Outcome { get; set; }
+    public DateTime? NextFollowupDate { get; set; }
+    public string? Notes { get; set; }
+    public DateTime CreatedAt { get; set; }
+    public DateTime UpdatedAt { get; set; }
+}
diff --git a/TaxBaik.Domain/Entities/Contract.cs b/TaxBaik.Domain/Entities/Contract.cs
new file mode 100644
index 0000000..9cf4a8a
--- /dev/null
+++ b/TaxBaik.Domain/Entities/Contract.cs
@@ -0,0 +1,19 @@
+namespace TaxBaik.Domain.Entities;
+
+public class Contract
+{
+    public int Id { get; set; }
+    public int ClientId { get; set; }
+    public string ContractNumber { get; set; } = "";
+    public string ServiceType { get; set; } = "";
+    public DateTime ContractDate { get; set; }
+    public DateTime StartDate { get; set; }
+    public DateTime? EndDate { get; set; }
+    public decimal? MonthlyFee { get; set; }
+    public decimal? TotalAmount { get; set; }
+    public string PaymentStatus { get; set; } = "pending";
+    public string Status { get; set; } = "active";
+    public string? Notes { get; set; }
+    public DateTime CreatedAt { get; set; }
+    public DateTime UpdatedAt { get; set; }
+}
diff --git a/TaxBaik.Domain/Entities/RevenueTracking.cs b/TaxBaik.Domain/Entities/RevenueTracking.cs
new file mode 100644
index 0000000..0916ef3
--- /dev/null
+++ b/TaxBaik.Domain/Entities/RevenueTracking.cs
@@ -0,0 +1,17 @@
+namespace TaxBaik.Domain.Entities;
+
+public class RevenueTracking
+{
+    public int Id { get; set; }
+    public int ClientId { get; set; }
+    public string InvoiceNumber { get; set; } = "";
+    public DateTime InvoiceDate { get; set; }
+    public string? ServiceType { get; set; }
+    public decimal Amount { get; set; }
+    public string PaymentStatus { get; set; } = "pending";
+    public DateTime? PaymentDate { get; set; }
+    public DateTime? DueDate { get; set; }
+    public string? Notes { get; set; }
+    public DateTime CreatedAt { get; set; }
+    public DateTime UpdatedAt { get; set; }
+}
diff --git a/TaxBaik.Domain/Entities/TaxFilingSchedule.cs b/TaxBaik.Domain/Entities/TaxFilingSchedule.cs
new file mode 100644
index 0000000..ae4c1ef
--- /dev/null
+++ b/TaxBaik.Domain/Entities/TaxFilingSchedule.cs
@@ -0,0 +1,16 @@
+namespace TaxBaik.Domain.Entities;
+
+public class TaxFilingSchedule
+{
+    public int Id { get; set; }
+    public int ClientId { get; set; }
+    public string FilingType { get; set; } = "";
+    public DateTime DueDate { get; set; }
+    public int FilingYear { get; set; }
+    public string Status { get; set; } = "pending";
+    public int? AssignedToId { get; set; }
+    public DateTime? CompletedDate { get; set; }
+    public string? Notes { get; set; }
+    public DateTime CreatedAt { get; set; }
+    public DateTime UpdatedAt { get; set; }
+}
diff --git a/TaxBaik.Domain/Entities/TaxProfile.cs b/TaxBaik.Domain/Entities/TaxProfile.cs
new file mode 100644
index 0000000..9c9079e
--- /dev/null
+++ b/TaxBaik.Domain/Entities/TaxProfile.cs
@@ -0,0 +1,21 @@
+namespace TaxBaik.Domain.Entities;
+
+public class TaxProfile
+{
+    public int Id { get; set; }
+    public int ClientId { get; set; }
+    public string? BusinessRegistration { get; set; }
+    public string? BusinessType { get; set; }
+    public DateTime? EstablishmentDate { get; set; }
+    public string? AnnualRevenueRange { get; set; }
+    public int? EmployeeCount { get; set; }
+    public string? AccountingMethod { get; set; }
+    public string? FiscalYearEnd { get; set; }
+    public DateTime? LastFilingDate { get; set; }
+    public DateTime? NextFilingDueDate { get; set; }
+    public string TaxRiskLevel { get; set; } = "normal";
+    public bool PreviousAuditHistory { get; set; }
+    public string? SpecialNotes { get; set; }
+    public DateTime CreatedAt { get; set; }
+    public DateTime UpdatedAt { get; set; }
+}
diff --git a/TaxBaik.Domain/Interfaces/IConsultingActivityRepository.cs b/TaxBaik.Domain/Interfaces/IConsultingActivityRepository.cs
new file mode 100644
index 0000000..2a71662
--- /dev/null
+++ b/TaxBaik.Domain/Interfaces/IConsultingActivityRepository.cs
@@ -0,0 +1,12 @@
+namespace TaxBaik.Domain.Interfaces;
+
+using TaxBaik.Domain.Entities;
+
+public interface IConsultingActivityRepository
+{
+    Task<int> CreateAsync(ConsultingActivity activity, CancellationToken cancellationToken = default);
+    Task<IEnumerable<ConsultingActivity>> GetByClientIdAsync(int clientId, CancellationToken cancellationToken = default);
+    Task<IEnumerable<ConsultingActivity>> GetPendingFollowupsAsync(CancellationToken cancellationToken = default);
+    Task<IEnumerable<ConsultingActivity>> GetByConsultantAsync(int consultantId, DateTime fromDate, CancellationToken cancellationToken = default);
+    Task UpdateAsync(ConsultingActivity activity, CancellationToken cancellationToken = default);
+}
diff --git a/TaxBaik.Domain/Interfaces/IContractRepository.cs b/TaxBaik.Domain/Interfaces/IContractRepository.cs
new file mode 100644
index 0000000..7815545
--- /dev/null
+++ b/TaxBaik.Domain/Interfaces/IContractRepository.cs
@@ -0,0 +1,14 @@
+namespace TaxBaik.Domain.Interfaces;
+
+using TaxBaik.Domain.Entities;
+
+public interface IContractRepository
+{
+    Task<int> CreateAsync(Contract contract, CancellationToken cancellationToken = default);
+    Task<Contract?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<IEnumerable<Contract>> GetByClientIdAsync(int clientId, CancellationToken cancellationToken = default);
+    Task<IEnumerable<Contract>> GetActiveContractsAsync(CancellationToken cancellationToken = default);
+    Task<IEnumerable<Contract>> GetExpiringContractsAsync(int daysAhead = 30, CancellationToken cancellationToken = default);
+    Task UpdateAsync(Contract contract, CancellationToken cancellationToken = default);
+    Task<decimal> GetMonthlyRecurringRevenueAsync(CancellationToken cancellationToken = default);
+}
diff --git a/TaxBaik.Domain/Interfaces/IRevenueTrackingRepository.cs b/TaxBaik.Domain/Interfaces/IRevenueTrackingRepository.cs
new file mode 100644
index 0000000..f1a04aa
--- /dev/null
+++ b/TaxBaik.Domain/Interfaces/IRevenueTrackingRepository.cs
@@ -0,0 +1,14 @@
+namespace TaxBaik.Domain.Interfaces;
+
+using TaxBaik.Domain.Entities;
+
+public interface IRevenueTrackingRepository
+{
+    Task<int> CreateAsync(RevenueTracking revenue, CancellationToken cancellationToken = default);
+    Task<IEnumerable<RevenueTracking>> GetByClientIdAsync(int clientId, CancellationToken cancellationToken = default);
+    Task<IEnumerable<RevenueTracking>> GetPendingPaymentsAsync(CancellationToken cancellationToken = default);
+    Task<IEnumerable<RevenueTracking>> GetByDateRangeAsync(DateTime startDate, DateTime endDate, CancellationToken cancellationToken = default);
+    Task UpdateAsync(RevenueTracking revenue, CancellationToken cancellationToken = default);
+    Task MarkPaidAsync(int id, DateTime paymentDate, CancellationToken cancellationToken = default);
+    Task<decimal> GetTotalRevenueAsync(DateTime startDate, DateTime endDate, CancellationToken cancellationToken = default);
+}
diff --git a/TaxBaik.Domain/Interfaces/ITaxFilingScheduleRepository.cs b/TaxBaik.Domain/Interfaces/ITaxFilingScheduleRepository.cs
new file mode 100644
index 0000000..5bfefd2
--- /dev/null
+++ b/TaxBaik.Domain/Interfaces/ITaxFilingScheduleRepository.cs
@@ -0,0 +1,14 @@
+namespace TaxBaik.Domain.Interfaces;
+
+using TaxBaik.Domain.Entities;
+
+public interface ITaxFilingScheduleRepository
+{
+    Task<int> CreateAsync(TaxFilingSchedule schedule, CancellationToken cancellationToken = default);
+    Task<TaxFilingSchedule?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TaxFilingSchedule>> GetByClientIdAsync(int clientId, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TaxFilingSchedule>> GetUpcomingDuesAsync(int daysAhead = 30, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TaxFilingSchedule>> GetByStatusAsync(string status, CancellationToken cancellationToken = default);
+    Task UpdateAsync(TaxFilingSchedule schedule, CancellationToken cancellationToken = default);
+    Task MarkCompletedAsync(int id, CancellationToken cancellationToken = default);
+}
diff --git a/TaxBaik.Domain/Interfaces/ITaxProfileRepository.cs b/TaxBaik.Domain/Interfaces/ITaxProfileRepository.cs
new file mode 100644
index 0000000..970327e
--- /dev/null
+++ b/TaxBaik.Domain/Interfaces/ITaxProfileRepository.cs
@@ -0,0 +1,12 @@
+namespace TaxBaik.Domain.Interfaces;
+
+using TaxBaik.Domain.Entities;
+
+public interface ITaxProfileRepository
+{
+    Task<int> CreateAsync(TaxProfile profile, CancellationToken cancellationToken = default);
+    Task<TaxProfile?> GetByClientIdAsync(int clientId, CancellationToken cancellationToken = default);
+    Task UpdateAsync(TaxProfile profile, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TaxProfile>> GetByRiskLevelAsync(string riskLevel, CancellationToken cancellationToken = default);
+    Task<IEnumerable<TaxProfile>> GetUpcomingFilingDuesAsync(DateTime startDate, DateTime endDate, CancellationToken cancellationToken = default);
+}
diff --git a/db/migrations/V015__AddTaxProfileAndExtendClients.sql b/db/migrations/V015__AddTaxProfileAndExtendClients.sql
new file mode 100644
index 0000000..bfffa91
--- /dev/null
+++ b/db/migrations/V015__AddTaxProfileAndExtendClients.sql
@@ -0,0 +1,105 @@
+-- Extend clients table with tax-specific fields
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS business_registration_number VARCHAR(20);
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS business_type VARCHAR(50);
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS establishment_date DATE;
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS annual_revenue_range VARCHAR(50);
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS employee_count INT;
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS last_tax_filing_date DATE;
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS tax_risk_level VARCHAR(20) DEFAULT 'normal';
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS next_filing_due_date DATE;
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS contact_person VARCHAR(100);
+ALTER TABLE clients ADD COLUMN IF NOT EXISTS company_id INT REFERENCES companies(id) ON DELETE SET NULL;
+
+-- Create tax_profiles table for detailed tax information
+CREATE TABLE IF NOT EXISTS tax_profiles (
+    id                      SERIAL          PRIMARY KEY,
+    client_id               INT             NOT NULL UNIQUE REFERENCES clients(id) ON DELETE CASCADE,
+    business_registration   VARCHAR(20),
+    business_type           VARCHAR(50),
+    establishment_date      DATE,
+    annual_revenue_range    VARCHAR(50),
+    employee_count          INT,
+    accounting_method       VARCHAR(50),
+    fiscal_year_end         VARCHAR(10),
+    last_filing_date        DATE,
+    next_filing_due_date    DATE,
+    tax_risk_level          VARCHAR(20) DEFAULT 'normal',
+    previous_audit_history  BOOLEAN DEFAULT FALSE,
+    special_notes           TEXT,
+    created_at              TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at              TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Create tax_filing_schedules table for tracking schedules
+CREATE TABLE IF NOT EXISTS tax_filing_schedules (
+    id                      SERIAL          PRIMARY KEY,
+    client_id               INT             NOT NULL REFERENCES clients(id) ON DELETE CASCADE,
+    filing_type             VARCHAR(100)    NOT NULL,
+    due_date                DATE            NOT NULL,
+    filing_year             INT             NOT NULL,
+    status                  VARCHAR(50) DEFAULT 'pending',
+    assigned_to             INT             REFERENCES admin_users(id) ON DELETE SET NULL,
+    completed_date          DATE,
+    notes                   TEXT,
+    created_at              TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at              TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Create consulting_activities table for CRM (상담 활동 추적)
+CREATE TABLE IF NOT EXISTS consulting_activities (
+    id                      SERIAL          PRIMARY KEY,
+    client_id               INT             NOT NULL REFERENCES clients(id) ON DELETE CASCADE,
+    activity_type           VARCHAR(50)     NOT NULL,
+    activity_date           DATE            NOT NULL,
+    activity_time           TIME,
+    assigned_consultant     INT             REFERENCES admin_users(id) ON DELETE SET NULL,
+    description             TEXT            NOT NULL,
+    outcome                 VARCHAR(100),
+    next_followup_date      DATE,
+    notes                   TEXT,
+    created_at              TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at              TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Create contracts table (계약 관리)
+CREATE TABLE IF NOT EXISTS contracts (
+    id                      SERIAL          PRIMARY KEY,
+    client_id               INT             NOT NULL REFERENCES clients(id) ON DELETE CASCADE,
+    contract_number         VARCHAR(50)     NOT NULL UNIQUE,
+    service_type            VARCHAR(100)    NOT NULL,
+    contract_date           DATE            NOT NULL,
+    start_date              DATE            NOT NULL,
+    end_date                DATE,
+    monthly_fee             NUMERIC(10, 2),
+    total_amount            NUMERIC(10, 2),
+    payment_status          VARCHAR(50) DEFAULT 'pending',
+    status                  VARCHAR(50) DEFAULT 'active',
+    notes                   TEXT,
+    created_at              TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at              TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Create revenue_tracking table (매출 추적)
+CREATE TABLE IF NOT EXISTS revenue_tracking (
+    id                      SERIAL          PRIMARY KEY,
+    client_id               INT             NOT NULL REFERENCES clients(id) ON DELETE CASCADE,
+    invoice_number          VARCHAR(50)     NOT NULL UNIQUE,
+    invoice_date            DATE            NOT NULL,
+    service_type            VARCHAR(100),
+    amount                  NUMERIC(10, 2) NOT NULL,
+    payment_status          VARCHAR(50) DEFAULT 'pending',
+    payment_date            DATE,
+    due_date                DATE,
+    notes                   TEXT,
+    created_at              TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at              TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Create indexes for performance
+CREATE INDEX IF NOT EXISTS idx_clients_company ON clients(company_id);
+CREATE INDEX IF NOT EXISTS idx_tax_profiles_client ON tax_profiles(client_id);
+CREATE INDEX IF NOT EXISTS idx_tax_filing_schedules_client ON tax_filing_schedules(client_id);
+CREATE INDEX IF NOT EXISTS idx_tax_filing_schedules_due_date ON tax_filing_schedules(due_date);
+CREATE INDEX IF NOT EXISTS idx_consulting_activities_client ON consulting_activities(client_id);
+CREATE INDEX IF NOT EXISTS idx_contracts_client ON contracts(client_id);
+CREATE INDEX IF NOT EXISTS idx_revenue_tracking_client ON revenue_tracking(client_id);