Patent data provide an increasingly used means to analyse innovation performance worldwide including in countries with incomplete data coverage, such as some developing countries. This paper discusses the specific issues associated with using patent data for measuring and analysing innovation in narrow technological fields, such as many environment-related technologies. To improve cross-country comparability of patent statistics, the paper advocates the use of indicators based on patent family size because they are more flexible and can be adapted to various applications. The paper also examines certain idiosyncratic characteristics of patent databases and proposes approaches to mitigate potential biases in empirical cross-country analyses. While doing so is particularly important for analyses of narrow technological fields such as many environment- and climate-related technologies, some of these issues are relevant for patent analysis more broadly.