Stab-resistant armor has been receiving increasing attention in recent years. Armor designed to protect against threats such as bullets may not be effective against stabbing attacks, as the mechanisms of resistance to ballistic impact and stabbing differ significantly. Shear thickening fluid (STF) has emerged as a promising material for the development of stab and spike-resistant armor. This chapter provides a comprehensive overview of the applications of STF in the design and development of stab-resistant armor. It covers the fundamental principles of STF and highlights recent research findings in this evolving field.