Metal additive manufacturing (AM) processes have been receiving growing industrial attention in recent times for near net shape manufacture of complex parts with traditionally difficult-to-machine materials, such as high-performance super alloys and Titanium alloys. AM processing of these materials is especially promising for aerospace and other industrial sectors that value design flexibility, rapid production, and reduction in wastage of expensive feedstock. However, depending upon the specific AM technique employed, AM-built parts may be characterized by one or more of the following: defects, presence of undesirable phases, absence of desired hardening precipitates, anisotropy in properties, etc. Consequently, thermal post-treatment can be a crucial step in any robust production process aimed at ensuring that the AM-built components eventually meet critical service requirements. Depending upon the alloy in question, thermal post-treatments can comprise hot isostatic pressing and heat treatment. This chapter outlines the main drivers for thermal post-treatment in case of AM processed super alloys and Ti alloys, as well as the typical stages involved based on the alloy or application in question. The influence of each stage of post-treatment, as well as the associated time-temperature schedules, on microstructure, phase constitution, and mechanical properties is also discussed, using illustrative examples from AM-built Alloy 718 and Ti-6Al-4V.