Following a request from the European Food Safety Authority, the Panel on Plant Protection Products and their Residues developed an opinion on the science to support the development of a risk assessment scheme of plant (crop) protection products on non-target terrestrial plants (NTTPs). This scientific opinion is largely a literature review on the most up-to-date knowledge of factors influencing phytotoxicity testing and risk assessment of NTTPs. Specific protection goals (SPGs) were defined for off-field, in-field and endangered species. SPGs are closely linked to ecosystem services and functions, and include maintaining provision of water regulation, food web support, aesthetic values, genetic resources and biodiversity. Gaps were identified in standard guidelines currently used in lower tier testing (tier I/II). In these guidelines, tests are conducted at the seedling/juvenile stage using mostly annual crops, and effects are recorded at the juvenile/vegetative stage under greenhouse conditions with plants grown individually or in monoculture. Endpoints measured do not include the overall effect on the whole life cycle (germinating seeds, seedling, juvenile stages, flowering, and seed production and germinability). It is also noted that it is unknown whether the following groups of organisms are covered by the plant risk assessment as it is carried out now: ferns, mosses, liverworts, hornworts, horsetails, lichens or woody species. In terms of exposure, droplet drift is considered to be the most important factor for off-field emissions to non-target areas. Models are available to calculate loadings from spray drift. Higher tier assessment is not required if the risk based on the tier II level can be managed by risk mitigation measures. When required, higher tier tests should be conducted under more realistic conditions. They may include additional laboratory/greenhouse tests (e.g. to measure reproductive endpoints or species interactions), microcosms or field experiments with experimentally or already established species. Other issues were considered, including exposure to mixtures, adjuvants, co-formulants and metabolites. Recommendations for the improvement of current guidelines and the elaboration of new guidelines and risk assessment schemes are provided.