Title: Bockstein homomorphisms for Hochschild cohomology of group algebras and of block algebras of finite groups Authors: C.C. Todea; Abstract: We give an explicit approach for Bockstein homomorphisms of the Hochschild cohomology of a group algebra and of a block algebra of a finite group and we show some properties. To give explicit definitions for these maps we use an additive decomposition and a Product Formula for the Hochschild cohomology of group algebras given by Siegel and Witherspoon in 1999. For $k$ an algebraically closed field of characteristic $p$ and $G$ a finite group we prove an additive decomposition and a Product Formula for the cohomology algebra of a defect group of a block ideal of $kG$ with coefficients in the source algebra of this block, and we define similar Bockstein homomorphisms. Satus: Accepted/2016/ Forum Mathematicum