This chapter covers scientific contributions in quinquevalent organo-phosphorus chemistry published in the literature in 2020. The review is not comprehensive but shows the most important achievements in the area, contained in leading journals including selected articles from the Phosphorus, Sulphur, Silicon, and Related Elements journal. In this year, 346 publications have been selected from two databases Reaxys and CAS SciFinder versus 405 in the previous year. The chapter describes organo-phosphorus compounds containing three P–O bonds (section: phosphoric acids and their derivatives), two P–O and one P–C bonds (section: phosphonic acids and their derivatives) as well as one P–O and two P–C bonds (section: phosphinic acids and their derivatives), in addition to the phosphoryl group P═O. The corresponding hetero-analogs of phosphoric, phosphonic and phosphinic acids and their derivatives containing combinations of P–X and P═Y bonds (X,Y = O, N, S, Se) has also been described in the end of subsections. Each of the main sections has been divided in the same way, covering synthesis, reactions, biological aspects and miscellaneous applications, other than biological ones, of phosphoric, phosphonic and phosphinic acids and their derivatives. In order to increase the clarity of the reviewed material, this year the subsection division proposed last year has been maintained: “synthesis and reactions” covering pure synthesis without applications, “synthesis and biological applications” and “synthesis and miscellaneous applications” covering syntheses aimed at further non-biological applications.