Transition metal pnictides such as MnSb have interesting magnetic and magneto-transport properties and high potential in semiconductor spintronics. I will discuss molecular beam epitaxy growth of these materials on III-V semiconductor and Ge substrates, highlighting the analogies with III-V epitaxy. We have recently grown thick (tens of nm) epitaxial cubic polymorphs of MnSb on ordinary hexagonal MnSb, and the experimental evidence for the cubic phase will be reviewed. We predict cubic MnSb to be a robust half-metallic ferromagnet to beyond 300K, using a "disordered local moments" density functional approach, which allows non-zero temperature magnetic properties to be calculated from first principles. This will be compared to the classic half-metal NiMnSb, which probably loses its spin polarisation at much lower temperature.