diff --git a/backend/src/database/schema.sql b/backend/src/database/schema.sql
new file mode 100644
index 0000000..81c8e44
--- /dev/null
+++ b/backend/src/database/schema.sql
@@ -0,0 +1,198 @@
+PRAGMA foreign_keys = ON;
+
+-- Users table
+CREATE TABLE IF NOT EXISTS users (
+  id TEXT PRIMARY KEY,
+  email TEXT UNIQUE NOT NULL,
+  password_hash TEXT NOT NULL,
+  display_name TEXT NOT NULL,
+  role TEXT NOT NULL DEFAULT 'planner',
+  is_active INTEGER NOT NULL DEFAULT 1,
+  created_at TEXT,
+  updated_at TEXT
+);
+
+-- Sessions table
+CREATE TABLE IF NOT EXISTS sessions (
+  id TEXT PRIMARY KEY,
+  user_id TEXT NOT NULL REFERENCES users(id),
+  token_hash TEXT UNIQUE NOT NULL,
+  expires_at TEXT NOT NULL,
+  created_at TEXT,
+  ip_address TEXT,
+  user_agent TEXT
+);
+
+-- Projects table
+CREATE TABLE IF NOT EXISTS projects (
+  id TEXT PRIMARY KEY,
+  name TEXT NOT NULL,
+  description TEXT,
+  owner_id TEXT NOT NULL REFERENCES users(id),
+  units TEXT NOT NULL DEFAULT 'mm',
+  created_at TEXT NOT NULL DEFAULT datetime('now'),
+  updated_at TEXT NOT NULL DEFAULT datetime('now'),
+  thumbnail_path TEXT
+);
+
+-- Project members table
+CREATE TABLE IF NOT EXISTS project_members (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  user_id TEXT NOT NULL REFERENCES users(id),
+  role TEXT NOT NULL DEFAULT 'betrachter',
+  invited_at TEXT,
+  accepted_at TEXT,
+  UNIQUE(project_id, user_id)
+);
+
+-- Layers table
+CREATE TABLE IF NOT EXISTS layers (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  name TEXT NOT NULL,
+  visible INTEGER NOT NULL DEFAULT 1,
+  locked INTEGER NOT NULL DEFAULT 0,
+  color TEXT,
+  line_type TEXT,
+  transparency REAL NOT NULL DEFAULT 0.0,
+  sort_order INTEGER NOT NULL DEFAULT 0,
+  created_at TEXT
+);
+
+-- Elements table
+CREATE TABLE IF NOT EXISTS elements (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  layer_id TEXT REFERENCES layers(id),
+  element_type TEXT NOT NULL,
+  geometry TEXT NOT NULL,
+  style TEXT,
+  metadata TEXT,
+  created_at TEXT,
+  updated_at TEXT
+);
+
+-- Blocks table
+CREATE TABLE IF NOT EXISTS blocks (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  name TEXT UNIQUE NOT NULL,
+  base_element_ids TEXT NOT NULL,
+  created_at TEXT
+);
+
+-- Block instances table
+CREATE TABLE IF NOT EXISTS block_instances (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  block_id TEXT NOT NULL REFERENCES blocks(id) ON DELETE CASCADE,
+  layer_id TEXT REFERENCES layers(id),
+  position_x REAL NOT NULL,
+  position_y REAL NOT NULL,
+  rotation REAL NOT NULL DEFAULT 0.0,
+  scale_x REAL NOT NULL DEFAULT 1.0,
+  scale_y REAL NOT NULL DEFAULT 1.0,
+  created_at TEXT
+);
+
+-- Background images table
+CREATE TABLE IF NOT EXISTS background_images (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  file_path TEXT NOT NULL,
+  position_x REAL NOT NULL DEFAULT 0.0,
+  position_y REAL NOT NULL DEFAULT 0.0,
+  scale REAL NOT NULL DEFAULT 1.0,
+  rotation REAL NOT NULL DEFAULT 0.0,
+  opacity REAL NOT NULL DEFAULT 1.0,
+  created_at TEXT
+);
+
+-- Versions table
+CREATE TABLE IF NOT EXISTS versions (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  label TEXT,
+  description TEXT,
+  snapshot_data BLOB NOT NULL,
+  created_by TEXT REFERENCES users(id),
+  created_at TEXT
+);
+
+-- Plugins table
+CREATE TABLE IF NOT EXISTS plugins (
+  id TEXT PRIMARY KEY,
+  name TEXT UNIQUE NOT NULL,
+  version TEXT NOT NULL,
+  display_name TEXT NOT NULL,
+  description TEXT,
+  manifest TEXT NOT NULL,
+  is_active INTEGER NOT NULL DEFAULT 0,
+  installed_at TEXT,
+  activated_at TEXT
+);
+
+-- Settings table
+CREATE TABLE IF NOT EXISTS settings (
+  id TEXT PRIMARY KEY,
+  user_id TEXT REFERENCES users(id),
+  key TEXT NOT NULL,
+  value TEXT NOT NULL,
+  updated_at TEXT,
+  UNIQUE(user_id, key)
+);
+
+-- AI Config table
+CREATE TABLE IF NOT EXISTS ai_config (
+  id TEXT PRIMARY KEY,
+  scope TEXT NOT NULL,
+  project_id TEXT REFERENCES projects(id),
+  api_base_url TEXT,
+  api_key_encrypted TEXT,
+  model TEXT NOT NULL DEFAULT 'gpt-4o',
+  created_at TEXT,
+  updated_at TEXT
+);
+
+-- Webhooks table
+CREATE TABLE IF NOT EXISTS webhooks (
+  id TEXT PRIMARY KEY,
+  project_id TEXT NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
+  url TEXT NOT NULL,
+  event TEXT NOT NULL,
+  is_active INTEGER NOT NULL DEFAULT 1,
+  created_at TEXT
+);
+
+-- Audit log table
+CREATE TABLE IF NOT EXISTS audit_log (
+  id TEXT PRIMARY KEY,
+  user_id TEXT REFERENCES users(id),
+  project_id TEXT REFERENCES projects(id),
+  action TEXT NOT NULL,
+  details TEXT,
+  ip_address TEXT,
+  created_at TEXT
+);
+
+-- Indexes
+CREATE INDEX IF NOT EXISTS idx_sessions_user_id ON sessions(user_id);
+CREATE INDEX IF NOT EXISTS idx_sessions_token_hash ON sessions(token_hash);
+CREATE INDEX IF NOT EXISTS idx_projects_owner_id ON projects(owner_id);
+CREATE INDEX IF NOT EXISTS idx_project_members_project_id ON project_members(project_id);
+CREATE INDEX IF NOT EXISTS idx_project_members_user_id ON project_members(user_id);
+CREATE INDEX IF NOT EXISTS idx_layers_project_id ON layers(project_id);
+CREATE INDEX IF NOT EXISTS idx_elements_project_id ON elements(project_id);
+CREATE INDEX IF NOT EXISTS idx_elements_layer_id ON elements(layer_id);
+CREATE INDEX IF NOT EXISTS idx_blocks_project_id ON blocks(project_id);
+CREATE INDEX IF NOT EXISTS idx_block_instances_project_id ON block_instances(project_id);
+CREATE INDEX IF NOT EXISTS idx_block_instances_block_id ON block_instances(block_id);
+CREATE INDEX IF NOT EXISTS idx_background_images_project_id ON background_images(project_id);
+CREATE INDEX IF NOT EXISTS idx_versions_project_id ON versions(project_id);
+CREATE INDEX IF NOT EXISTS idx_versions_created_by ON versions(created_by);
+CREATE INDEX IF NOT EXISTS idx_settings_user_id ON settings(user_id);
+CREATE INDEX IF NOT EXISTS idx_ai_config_project_id ON ai_config(project_id);
+CREATE INDEX IF NOT EXISTS idx_webhooks_project_id ON webhooks(project_id);
+CREATE INDEX IF NOT EXISTS idx_audit_log_user_id ON audit_log(user_id);
+CREATE INDEX IF NOT EXISTS idx_audit_log_project_id ON audit_log(project_id);