The species/time relationship (STR) describes how the species richness of acommunity increases with the time span over which the community is observed. Thispattern has numerous implications for both theory and conservation in much the sameway as the species/area relationship (SAR). However, the STR has received much lessattention and to date only a handful of papers have been published on the pattern. Herewe gather together 984 community time-series, representing 15 study areas and ninetaxonomic groups, and evaluate their STRs in order to assess the generality of the STR,its consistency across ecosystems and taxonomic groups, its functional form, and itsrelationship to local species richness. In general, STRs were surprisingly similar acrossmajor taxonomic groups and ecosystem types. STRs tended to be well fit by bothpower and logarithmic functions, and power function exponents typically rangedbetween 0.2 and 0.4. Communities with high richness tended to have lower STRexponents, suggesting that factors increasing richness may simultaneously decreaseturnover in ecological systems. Our results suggest that the STR is as fundamental anecological pattern as the SAR, and raise questions about the general processesunderlying this pattern. They also highlight the dynamic nature of most speciesassemblages, and the need to incorporate time scale in both basic and applied researchon species richness patterns.