The Pt based alloys are anticipated to replace Ni- Based alloys which finds applications in modern jet turbine engines. The work in this book explores the Pt-Al-Nb system which has not been previously reported in literature. Samples above 40 at.% Pt were studied metallographically (using scanning electron microscopes) in the as-cast and heat treated conditions and the reaction schemes identified. The various phase and overall compositions were identified with energy dispersive X-ray spectrometry (EDS) and confirmed by X-ray diffraction (XRD). The book includes a guide in derivation of the liquidus surface which shows the primary phases that solidify, and the subsequent solidification reactions. The liquidus surface is later used be used to check the consistency of the results. The non trivial Solidification reactions in the as-cast alloys, partial experimental liquidus surface for the alloy system, Invariant reactions in the Pt-Al-Nb system, 1000°C isothermal section of the Pt-Al-Nb system are also included.