We evaluated the "4 per 1000″ initiative for increasing soil organic carbon (SOC) by analysing rates of SOC increase in treatments in 16 long-term experiments in south-east UK. The initiative sets a goal for SOC stock to increase by 4‰ yr-1 in the 0-40 cm soil depth, continued over 20 years. Our experiments, on 3 soil types, provided 114 treatment comparisons over 7-157 years. Treatments included organic additions (incorporated by inversion ploughing), N fertilizers, introducing pasture leys into continuous arable systems, and converting arable land to woodland. In 65% of cases, SOC increases occurred at >7‰ yr-1 in the 0-23 cm depth, approximately equivalent to 4‰ yr-1 in the 0-40 cm depth. In the two longest running experiments (>150 yrs) annual farmyard manure (FYM) applications at 35 t fresh material ha-1 (equivalent to approx. 3.2 t organic C ha-1 yr-1 ) gave SOC increases of 18 and 43‰ yr-1 in the 23cm depth during the first 20 years. Increases exceeding 7‰ yr-1 continued for 40-60 yrs. In other experiments, with FYM applied at lower rates or not every year, there were increases of 3-8‰ yr-1 over several decades. Other treatments gave increases between zero and 19‰ yr-1 over various periods. We conclude that there are severe limitations to achieving the "4 per 1000″ goal in practical agriculture over large areas. The reasons include (a) farmers not having the necessary resources (e.g. insufficient manure); (b) some, though not all, practices favouring SOC already widely adopted; (c) practices uneconomic for farmers - potentially overcome by changes in regulations or subsidies; (d) practices undesirable for global food security. We suggest it is more realistic to promote practices for increasing SOC based on improving soil quality and functioning as small increases can have disproportionately large beneficial impacts, though not necessarily translating into increased crop yield. This article is protected by copyright. All rights reserved.