Tamoxifen is a well-known antiestrogen used for the hormonotherapy of estrogen receptor positive breast cancer. In addition to its high affinity binding to the estrogen receptor (ER), tamoxifen binds with comparable affinity to the microsomal antiestrogen binding site (AEBS), and inhibits with a micromolar efficiency, protein kinase C (PKC), calmodulin (CaM)-dependent enzymes and Acyl CoenzymeA: Cholesterol Acyl Transferase (ACAT). Each of these tamoxifen targets might explain the genomic as well as non-genomic effects of tamoxifen. In this review, we will report current knowledge about the structural features of tamoxifen involved in this multiple targeting. These data provide a useful guide for the conception of selective ligands of ERs, AEBS, PKC, CaM or ACAT based on the chemical structure of tamoxifen.