There are 4 main types of APIs in Salesforce: REST API, SOAP API, Bulk API, and Streaming API. REST API uses HTTP methods to expose Salesforce functionality and supports both XML and JSON. SOAP API uses WSDL definitions and only supports XML. Bulk API is for loading and querying large amounts of data asynchronously. Streaming API uses a publish-subscribe model to send notifications when data changes. Each API is best suited to different use cases depending on requirements.