The renal Na/K/2Cl cotransporter (NKCC2, BSC1) is selectively expressed in the apical membrane of cells of the thick ascending limb of Henle (TAL) and macula densa. NKCC2-dependent salt transport constitutes the major apical entry pathway for transepithelial salt reabsorption in the TAL. Although NKCC2 is encoded by a single gene (Slc12a1), differential splicing of the NKCC2 pre-mRNA, results in the formation of several alternate transcripts. Thus, 3 full-length splice-isoforms of NKCC2 differ in their variable exon 4, resulting in transcripts for NKCC2B, NKCC2A and NKCC2F. In addition to full-length isoforms, variants with truncated C-terminal ends have been described. The various splice isoforms of NKCC2 differ in their localization along the TAL and in their transport characteristics. Data in the literature are reviewed to assess the principles of NKCC2 differential splicing, the localization of NKCC2 splice isoforms along the TAL in various species, and the functional characteristics of the splice isoforms. In addition, we will discuss the functional significance of NKCC2 isoforms for TAL salt retrieval and for the specific salt sensor function of macula densa cells based on studies using isoform-specific NKCC2 knockout mice. We suggest that different NKCC2 splice variants cooperate in salt retrieval along the TAL and that the co-expression of two splice variants (NKCC2B and NKCC2A) in the macula densa cells facilitates efficient salt sensing over wide ranges of fluctuating salt concentrations.