Integration testing is a process that tests the interfaces between integrated software modules or units. It aims to expose faults in their interaction by deploying modules together and tracking defects from test results. There are various challenges like managing complex integration between new and legacy systems from different companies. Different types of incremental approaches include top-down, bottom-up, and sandwich methods, as well as a big bang approach for small systems. Integration testing provides benefits like early testing, detecting interface errors, and improving test coverage and reliability.