jRCaMP1b is a bright red genetically encoded fluorescent Ca[2+] indicator. It is a fusion protein composed of the calmodulin-binding M13 peptide, a circularly permuted red fluorescent protein and calmodulin. The circularly permuted fluorescent protein is based on mRuby and contains the amino acid substitutions T46W, I60N, L326M and R368G relative to its progenitor RCaMP1h. jRCaMP1b provides an improved signal-to-noise ratio, faster decay time and may be used in combination with ChR2 (FBrf0232227).