The book "Trends and Applications in Knowledge Discovery and Data Mining" offers a comprehensive collection of revised contributions that emerged from the workshops of the 23rd Pacific-Asia Conference on Knowledge Discovery and Data Mining (PAKDD 2019) held in Macau, China. This conference, which took place in April 2019, brought together professionals and researchers to discuss the latest developments and applications in the field of knowledge discovery and data analysis. The 31 selected and carefully reviewed articles come from various workshops addressing topics such as intelligent security, weakly supervised learning methods, data representation for clustering, biologically inspired techniques, and deep learning for knowledge transfer. This book is a valuable resource for scientists, practitioners, and students who wish to engage with current trends and challenges in data science.