Environmental isotopes and water quality indicators (e.g. TDS and NO₃ contents) were used to characterize the age, recharge history and controls on the quality of groundwater resources in the Yuncheng Basin, north China, where extensive extraction occurs for agriculture and domestic supply. δ¹⁸O and δ²H values as low as −10.6‰ and −73‰, respectively, together with low radiocarbon activities (<20pmC) show that deep groundwater comprises palaeowaters largely recharged in the late Pleistocene (∼10 to 22ka B.P.) under a cooler climate than the present. Shallow groundwater has higher radiocarbon activities (>70pmC), indicating a significant component of modern (post-1950s) recharge. The shallow groundwater has higher δ¹⁸O and δ²H values (up to −8.1‰ and −54‰) that are similar to those in modern summer monsoon rainfall, indicating that current recharge is via direct infiltration and/or leakage of ephemeral streams during heavy rain events. Historic recharge rates estimated using radiocarbon ages are between 1 and 10mm/year, corresponding to <2% of local rainfall, which is lower than estimates of modern recharge nearby based on tritium data. The relationship between groundwater δ¹⁸O values and ¹⁴C ages is similar to that observed in groundwater from other basins in northern China, confirming that much deep groundwater in the region is palaeowater, and suggesting that a broad scale assessment of groundwater residence times may be made from δ¹⁸O and δ²H values. Most deep groundwater has low TDS and nitrate concentrations (median 1090mg/L and 1.8mg/L, respectively), while shallow groundwater has TDS contents of up to 8450mg/L (median 2010mg/L) and NO₃ concentrations up to 630mg/L (median 31mg/L). A lack of enrichment in δ¹⁸O values in the high salinity shallow groundwater indicates that transpiration by crops and possibly minor mineral dissolution are the major salinisation processes, rather than evaporation or leakage from salt lakes. The majority of nitrate in groundwater has δ¹⁵N _NO3 values between 0.8‰ and 5.0‰ and δ¹⁸O_NO3 values between 1.8‰ and 4.1‰, indicating that synthetic fertilizers are the main source of elevated NO₃ concentrations. Increasing residence times from east-to-west in deep groundwaters reflect the historic regional flow pattern in the basin. However, present-day flow is now dictated by a large cone of depression that has formed due to intensive deep groundwater pumping since the 1980s. High downward vertical hydraulic gradients (up to 0.45) have also developed as a result of this pumping, promoting downwards leakage of shallow water, indicated by high nitrate concentrations (>20mg/L) in some deep wells (>180m). Preferential leakage has occurred near the Linyi fault, in the northern Sushui River Basin. Salinisation, nitrate contamination and excessive drawdown of deep groundwater are major concerns for the future of the groundwater resources in this region.