Activation of signal transduction pathways triggered in the parasite and the host cell, leading to intracellular Ca2+ mobilization, Ca2+-induced reorganization of the host cell actin cytoskeleton and lysosome recruitment, constitutes the general mechanism by which T. cruzi trypomastigotes invade mammalian cells. With a plethora of T. cruzi molecules that have been identified and characterized structural and functionally, plus the identification of target cell components involved, the whole process is beginning to be understood at the molecular level. The picture is complex. Not only MT and TCT engage different molecules to interact with host cells, but different T. cruzi isolates may use distinct sets of molecules, activating distinct signaling pathways. In addition, some molecular interactions may trigger inhibitory signals that down regulate trypomastigote invasion. Furthermore, as the in vivo infection is concerned, the interaction of parasites with host components before reaching the target cells has also to be considered. Great progress has been made towards understanding the mammalian cell invasion by T. cruzi, but a lot more work has to be done before we can draw a more complete and detailed picture of that process.