“…Particular interest has been paid to the positive-parity charm-strange mesons D * s0 (2317) and D s1 (2460) observed in 2003 by the BaBar (Aubert et al, 2003) and CLEO (Besson et al, 2003) Collaborations. The masses of D * s0 (2317) and D s1 (2460) are below the DK and D * K thresholds, respectively, by about the same amount, only 45 MeV (see Table I and references therein), which makes them natural candidates for hadronic molecules (Albaladejo et al, 2016c;Barnes et al, 2003;van Beveren and Rupp, 2003;Cleven et al, 2014aCleven et al, , 2011bFaessler et al, 2007;Flynn and Nieves, 2007;Gamermann et al, 2007;Guo et al, 2007Guo et al, , 2006Hofmann and Lutz, 2004;Kolomeitsev and Lutz, 2004;Szczepaniak, 2003;, while also other explanations such as P -wave cs states and tetraquarks exist in the literature. We will come back to the properties of these states occasionally in this review.…”