The deformation behavior of single-phase metastable beta-titanium alloys and two-phase alpha+metastable-beta alloys strongly depends on the degree of stability of the beta-phase. Recently, it has been shown that the tensile deformation behavior, as well as the creep deformation behavior at low temperatures (< 0.25T (m)), is strongly influenced by the degree of metastability. For example, the titanium beta-alloy Ti-13.0wt%Mn, which has higher stability than the titanium beta-alloy Ti-14.8wt%V, deforms by slip only; whereas the latter deforms by slip and twinning. In addition to the mechanical properties, the deformation mechanisms also depend on the degree of metastability. Further, the deformation mechanisms of a given metastable beta-alloy depend on whether the beta-phase is present by itself as a single-phase alloy, or in the presence of alpha-phase in the form of a two-phase alloy. For example, it was found that a metastable Ti-V alloy deforms by slip and twinning when it is in the form of a single-phase alloy, but deforms by slip and martensitic transformation when the same metastable beta-phase is present in a two-phase alpha + beta alloy. The mechanical properties of the metastable beta alloys in turn depend on these deformation mechanisms. These recent developments are reviewed in this article.