Trade surveillance refers to the monitoring of trading activity in financial markets to detect and prevent suspicious patterns, including market manipulation, fraud, and other abusive behaviors. This includes:

1. _Real-time monitoring_: Continuously tracking trading activity as it occurs.

2. _Pattern recognition_: Identifying unusual or suspicious trading patterns.

3. _Anomaly detection_: Flagging trades that deviate from normal market behavior.

4. _Trade reconstruction_: Rebuilding trades to identify potential manipulation.

5. _Investigations_: Conducting in-depth analyses of suspicious activity.

Trade surveillance is crucial to:

1. _Maintain market integrity_: Ensuring fair and orderly markets.

2. _Prevent market manipulation_: Detecting and deterring manipulative activities.

3. _Protect investors_: Safeguarding against fraudulent or abusive practices.

4. _Comply with regulations_: Meeting regulatory requirements and standards.

5. _Enhance market transparency_: Providing insights into market activity and behavior.

Trade surveillance is conducted by:

1. _Exchanges_: Self-regulatory organizations (SROs) like stock exchanges.

2. _Regulators_: Government agencies like the Securities and Exchange Commission (SEC).

3. _Broker-dealers_: Firms that facilitate trading and are responsible for monitoring their customers' activity.

4. _Market surveillance firms_: Specialized companies that provide trade surveillance services.

By leveraging advanced technologies like machine learning, artificial intelligence, and data analytics, trade surveillance helps to identify and prevent potentially harmful trading activities, promoting a fair and transparent market environment.