This paper deals with the plastic deformation mechanisms and the microstructural evolution of pure titanium sheets during Single Point Incremental Forming process (SPIF). Microstructural evolutions induced by SPIF are compared with those induced by monotonic plane strain stretching obtained by tensile tests. For monotonic straining, deformation mechanisms observed are mainly dislocation glide generally prismatic < a > and pyramidal < a > and < c+a >. whereas in SPIF straining, dislocation gliding and deformation twinning coexist. Slip systems involved in SPIF process are prismatic < a >, basal < a >, and first order pyramidal < a > and < c+a >. The twinning mode \11-22\ < 11-2-3 > was observed. This particular deformation mechanism could be explained by high strain rates and through-thickness compressive stress occuring during forming. It implies that models of plasticity developed thanks to conventional or heterogeneous tensile tests cannot provide a good description of the material behavior during this forming process.