diff --git a/src/shared/errors/index.ts b/src/shared/errors/index.ts
new file mode 100644
index 0000000..ad6fb05
--- /dev/null
+++ b/src/shared/errors/index.ts
@@ -0,0 +1,73 @@
+/**
+ * Base domain error class for all application-specific errors.
+ * Extends the built-in Error with a fixed name property for reliable
+ * instance checking across layers.
+ */
+export class DomainError extends Error {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'DomainError';
+  }
+}
+
+/**
+ * Thrown when a requested file cannot be found in storage.
+ */
+export class FileNotFoundError extends DomainError {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'FileNotFoundError';
+  }
+}
+
+/**
+ * Thrown when a requested bucket does not exist.
+ */
+export class BucketNotFoundError extends DomainError {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'BucketNotFoundError';
+  }
+}
+
+/**
+ * Thrown when a file exceeds the maximum allowed size for upload.
+ */
+export class FileTooLargeError extends DomainError {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'FileTooLargeError';
+  }
+}
+
+/**
+ * Thrown when an attempt is made to upload a file that already exists
+ * (detected by content hash deduplication).
+ */
+export class DuplicateFileError extends DomainError {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'DuplicateFileError';
+  }
+}
+
+/**
+ * Thrown when authentication fails or a valid session is not present.
+ */
+export class AuthenticationError extends DomainError {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'AuthenticationError';
+  }
+}
+
+/**
+ * Thrown when input validation fails (e.g. missing required fields,
+ * invalid format, or constraint violations).
+ */
+export class ValidationError extends DomainError {
+  constructor(msg: string) {
+    super(msg);
+    this.name = 'ValidationError';
+  }
+}
\ No newline at end of file
diff --git a/src/shared/logger/index.ts b/src/shared/logger/index.ts
new file mode 100644
index 0000000..36eda38
--- /dev/null
+++ b/src/shared/logger/index.ts
@@ -0,0 +1,33 @@
+import winston from 'winston';
+
+/**
+ * Application-wide logger singleton configured with Winston.
+ *
+ * Writes error-level logs to `logs/error.log`, all logs to
+ * `logs/combined.log`, and outputs to the console in both
+ * development (colorized, simple format) and production
+ * (JSON format) environments.
+ */
+const logger = winston.createLogger({
+  level: process.env.LOG_LEVEL || 'info',
+  format: winston.format.combine(
+    winston.format.timestamp(),
+    winston.format.errors({ stack: true }),
+    winston.format.json(),
+  ),
+  defaultMeta: { service: 'filedrop' },
+  transports: [
+    // Write all logs including error logs to file
+    new winston.transports.File({ filename: 'logs/error.log', level: 'error' }),
+    new winston.transports.File({ filename: 'logs/combined.log' }),
+    // Console transport for docker logs / CLI visibility
+    new winston.transports.Console({
+      format:
+        process.env.NODE_ENV !== 'production'
+          ? winston.format.combine(winston.format.colorize(), winston.format.simple())
+          : winston.format.json(),
+    }),
+  ],
+});
+
+export default logger;
\ No newline at end of file