This paper discusses the increasingly prominent role of ChatGPT in providing feedback and assessment for L2 writing in the digital age. It reviews representative studies that address five research strands about the use of ChatGPT in L2 writing contexts. After a critical evaluation of the existing literature, the author extensively explains four innovative sub-topics on leveraging ChatGPT for L2 writing feedback and assessment, drawing on multiple creative projects undertaken by her research team. These include: 1) ChatGPT-student collaboration in the L2 writing process; 2) ChatGPT-supported teacher feedback; 3) collaborative processing of ChatGPT feedback; and 4) the potential of ChatGPT for L2 writing assessment. This paper also addresses the importance of teacher training on the use of GenAI in language and writing instruction.