We assessed feeding and growth of the common jellyfish Aurelia aurita and 2 hydromedusae, Sarsia tubulosa and Aequorea vitrina, by examining the effect of temperature, medusa size, prey concentration and prey species on feeding and growth. In growth experiments with A. aurita ephyrae fed different species and concentrations of prey organisms (Artemia sp., Balanus sp., Brachionus sp., Rathkea octopunctata), the specific growth rate increased with increasing prey concentration, and a maximum specific growth rate of about 0.22 d-1 was obtained. For A. aurita medusae fed Acartia tonsa and Artemia sp., maximum growth was about 0.08 d-1. The minimum prey concentration resulting in maximum growth rate was 80 to 100 μg C l-1 for ephyrae (depending on prey type), and about 100 μg C l-1 for medusae. For S. tubulosa fed different prey concentrations of A. tonsa nauplii, the maximum specific growth rates were 0.32 and 0.1 d-1 for 2 and 4 mm individuals, respectively, achieved at prey concentrations between 15 and 30 μg C l-1. Maximum growth rates decreased with initial size in A. aurita and A. vitrina, to become approximately constant at 0.05 to 0.06 d -1. Clearance rates (F, l d-1) of A. aurita offered different prey types increased as a function of the umbrella diameter (D, mm) squared, expressed as F = aD2, where a-value depends on prey type. Both maximum specific growth rate and clearance rate increased exponentially with temperature between 4 and 19°C for ephyrae, and between 8 and 19°C for medusae, but at higher temperatures both growth and clearance decreased markedly. From experiments with A. aurita (both ephyra and medusae) in which growth, ingestion and respiration were measured simultaneously, carbon budgets were constructed for individuals growing at maximum rates when feeding on different prey types. Assimilation efficiency, net growth efficiency, and minimum concentrations of prey organisms needed for sustaining maximum growth were estimated, allowing evaluation of the degree to which jellyfish realize their growth potential in the field, or whether the jellyfish are controlling the zooplankton.