Conwy County Borough Council was preparing its Replacement Local Development Plan in 2019 and commissioned RHD Consultancy Ltd to work on a series of Welsh language impact assessments. We reviewed the existing Welsh language planning policy and undertook research into the revised Technical Advice Note 20, as well as recent developments in legislation and planning policy including Planning Policy Wales (2018). This work informed our development of a new Welsh language planning policy. Using statistical analysis, we identified the sites that are strategically important for the Welsh language and also developed an innovative approach to impact assessing the sites coming forward for planning. We undertook a thorough impact assessment of the Preferred Strategy and of individual proposed sites for development. Our Welsh language impact assessment was published alongside the Preferred Strategy for consultation, as part of the statutory planning process.