In the past, little attention was paid to the effects of the high β fraction retained at room temperature on the deformation behavior of β metastable titanium alloys. As it significantly differs from more conventional α/β alloys, mostly constituted of α phase, a thorough investigation appears as mandatory. This is the aim of the present study through a detailed characterization of the operating deformation processes combined with an evaluation of the strain field heterogeneities. Tensile tests conducted in a scanning electron microscope coupled with markers tracking and electron back-scattered diffraction techniques enabled an in situ monitoring of the early activity of deformation systems. A major influence of the elastic anisotropy of the β phase on the highly heterogeneous deformation behavior was revealed in the elastic and plastic regimes. The underlying mechanisms controlling the onset and the development of plasticity in β metastable titanium alloys are clarified and discussed accordingly.