This book constitutes the refereed proceedings of the 5th Multidisciplinary International Symposium on Disinformation in Open Online Media, MISDOOM 2023, which was held in Amsterdam, The Netherlands, during November 21–22, 2023. The 13 full papers presented in this book were carefully reviewed and selected from 19 submissions. The papers focus on misinformation, disinformation, hate speech, disinformation campaigns, social network analysis, large language models, generative AI, and multi-modal embeddings.