This provides an overview of the main developments in the teaching and learning of Welsh as a first language in the secondary schools of Wales during the last thirty years. It analyses the principles and theories that underpin the main teaching schemes that have been developed in this particular field (such as the ‘Gorwelion' project of the Schools Council in the 1970s that considerably influenced the teaching and learning of Welsh in the ‘modern' period), showing how they reflect some of the basic principles of the Bullock Report (1975) and the Whole Language movement – specifically the theory that suggests that language competence grows incrementally through an interaction of speaking and listening, reading, writing and experience. It goes on to analyse the main characteristics of children's writing in Welsh at Key Stage 3 by examining examples of children's work from across Wales. The main errors (or ‘miscues') are categorized, showing that models for the development of writing are found in the texts that children read, with the conclusion that the writing process must be developed side by side with reading. It advocates that children learn so much about writing from reading that teachers should base their teaching of writing on the ‘visual' elements of the texts that children read. The chapter concludes by outlining an agenda for the effective teaching of writing in Welsh to pupils at Key Stage 3, accenting the importance of the interaction of the different language modes, in particular reading and writing.