Process for installing an offshore tower, comprising: a) manufacturing a foundation comprising a block, manufacturing at least one superposition section of a shaft, and manufacturing a base section of a shaft; b) applying said base section to said foundation block (starting unit) to assume the relative position for the installed condition, applying said superposition sections to said starting unit in a multi-layered configuration, and applying lifting means to at least one of said foundation block and said base section; c) moving said starting unit up to the installation point; d) introducing ballast in said foundation block so that said starting unit sinks until resting on the bottom of the body of water; e) actuating said lifting means to expand said sections into the installed condition; f) between step a) and c), placing said foundation block or starting unit in the body of water of the installation point.