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Aims: To quantify changes in (i) potency (concentration of Δ 9 -tetrahydrocannabinol; %THC), (ii) price (euros/g of cannabis) and (iii) value (mg THC/euro) of cannabis resin and herbal cannabis in Europe., Design: Repeated cross-sectional study., Setting and Participants: Data collected from 28 European Union (EU) member states, Norway and Turkey by the European Monitoring Centre for Drugs and Drug Addiction., Measurements: Outcome variables were potency, price and value for cannabis resin and herbal cannabis in Europe, 2006-16. Inflation was estimated using the Harmonised Indices of Consumer Prices. Mixed-effects linear regression models were used to estimate linear and quadratic time trends, with a random intercept and slope fitted to account for variation across countries., Findings: Resin potency increased from a mean [95% confidence interval (CI)] of 8.14% THC (6.89, 9.49) in 2006 to 17.22 (15.23, 19.25) in 2016. Resin price increased from 8.21 euros/g (7.54, 8.97) to 12.27 (10.62, 14.16). Resin increased in value, from 11.00 mg THC per euro (8.60, 13.62) to 16.39 (13.68, 19.05). Quadratic time trends for resin potency and value indicated minimal change from 2006 to 2011, followed by marked increases from 2011 to 2016. Herbal cannabis potency increased from 5.00% THC (3.91, 6.23) to 10.22 (9.01, 11.47). Herbal price increased from 7.36 euros/g (6.22, 8.53) to 12.22 (10.59, 14.03). The value of herbal cannabis did not change from 12.65 mg of THC per euro (10.18, 15.34) to 12.72 (10.73, 14.73). All price trends persisted after adjusting for inflation., Conclusions: European cannabis resin and herbal cannabis increased in potency and price from 2006 to 2016. Cannabis resin (but not herbal cannabis) increased in the quantity of Δ 9 -tetrahydrocannabinol per euro spent. Marked increases in resin potency and value from 2011 to 2016 are consistent with the emergence of new resin production techniques in European and neighbouring drug markets., (© 2018 The Authors. Addiction published by John Wiley & Sons Ltd on behalf of Society for the Study of Addiction.)