Salesforce provides various APIs so that developers can easily integrate across Salesforce:
REST –  With the help of REST API you can easily incorporate Salesforce applications using HTTP methods in either XML or JSON formats. It is the most suitable choice for developing mobile applications or external clients.
Bulk – The Bulk API provides us programmatic access especially for quickly loading and querying large amounts of data into your Salesforce organization.
Streaming – The Streaming API is used to trigger and receive notifications whenever changes are made into Salesforce data, according to the defined criteria.