Both web developers and native application developers will occasionally need to use APIs. APIs are used to control the integration between a software product to another software product. For example, the popular payment processor and payment gateway PayPal has an API through which developers can connect to PayPal and process payments. Salesforce, a leading customer relationship management solution, has an API so that other products (such as enterprise resource management products) can connect to its data. While APIs may not apply in simple programming or development, they remain critically important to more advanced systems. Any programmer should be familiar with APIs, even though they may not be familiar with a specific API. Most APIs will come with their own documentation and training.