This presentation deals with input processing theory (hereafter IP theory) of VanPatten (2002a, 2002b, 2004, and 2009) and VanPatten and a number of his collaborates (e.g. VanPatten and Cadierno, 1993a, and 1993b; Wong and VanPatten, 2003). For this it explains the importance of input in discussions of language learning especially the learning of a second or foreign language. Then an elaboration of IP theory will be presented, theoretical and pedagogical implications of this theory for second language acquisition (SLA) will be pinpointed, and finally criticisms on IP will be discussed.