This study collates existing data on physiological maturity of female European Lobster Homarus gammarus across the North East Atlantic, together with new data from Orkney, Wales, and the Isle of Man. Using a standardised methodology, physiological estimates of size at maturity were undertaken using 1,309 lobsters from eleven locations. Size at 50% maturity varied between populations, ranging from 81.3 -94.1mm carapace length. Generalised Additive Models were used to characterise geographic patterns in size at maturity. Optimum monthly sea surface temperature (OPTIMNTH) had a significant and non-linear effect on the probability of being sexually mature at a given size in different populations. This is consistent with a thermal optimum previously demonstrated in absolute growth.