What is the difference between complacent and complaisant?

Complaisant means 'eager to please' and 'showing a cheerful willingness to fulfill others' wishes'. Complacent is quite the opposite, 'being pleased with oneself; contented to a fault'. However, they share one meaning, which may cause them to be confused - each also carries the sense of 'obliging, agreeable'. One could differentiate the two words by saying that complaisant is the active adverb and complacent denotes a more passive feeling. Complaisant was first recorded in 1647, deriving from Latin complacere. Complacent comes from the same Latin word, but is not found in writing until 1660.

Courtesy of Dictionary.com