Display omitted •This article summarizes the significant advances achieved in the past few years on synthesis, classification, mechanism and applications of CDs and CDs-based photocatalysts to give a thorough summary.•CDs-derived photocatalysts are devided into pure CDs and CDs composite photocatalysts and the photocatalytic efficiencies are compared.•Various kinds of mechanism during photocatalytic process in typical systems are concluded.•Applications in the fields of degradation of organics, water splitting for H2 and O2 evolution, CO2 conversion and photocatalytic chemical reactions are also reviewed to confirm the great potential of CDs-derived photocatalysts for environmental and energy issues. With the rapid development of science and technology, environmental pollution and energy shortage become more and more prominent. To solve these problems, photocatalytic technology is regarded as one of the most efficient methods, allowing for both pollutant degradation and energy conversion. Compared with traditional group IIVI, IIIV quantum dots (QDs), carbon dots (CDs), as a newly emerging kind of fluorescent carbon-based material, possess many excellent properties, such as high aqueous solubility, low cost, low toxicity, abundant surface functional groups and good biocompatibility. In particular, the unique up-converted photoluminescence (PL) behavior and photo-induced electron transfer ability of CDs provide the new route to achieve efficient metal-free photocatalysts. This article reviews recent progress on CDs utilized for photocatalysis from different perspectives, including the following three parts: classification and synthesis, mechanism of CDs-derived photocatalysts as well as the applications for environmental issues (up-converted PL process) and energy conversion (photo-induced electron transfer process).