This book constitutes the refereed proceedings of the 17th International Symposium on Advanced Parallel Processing Technologies, APPT 2026, held in Brussels, Belgium, on July 27, 2026.The 36 full papers, 11 Poster Papers and 4 work in- progress papers included in this book were carefully reviewed and selected from 135 submissions. They were organized in topical sections as follows: Featured Articles; LLM Inference; Serving Systems; LLM Workflows; AI Design Automation; Scalable Computing; AI Accelerators; Kernel Acceleration; Streaming Accelerators; Secure Systems; Data Efficiency; Poster and Work-in-Progress Papers.