This special issue is dedicated to selected papers from those presented at the 17th Algorithms and Data Structures Symposium (WADS 2021), which was held from August 9–11 fully online. WADS, which alternates with the Scandinavian Symposium and Workshops on Algorithm Theory (SWAT), is a forum for researchers in the area of design and analysis of algorithms and data structures.

In response to the call for papers, 123 papers were submitted from which the program committee selected 47 for presentation at WADS 2021. From these 47 papers, the program committee further selected four outstanding papers for their importance to algorithms research. The extended versions of these four papers, which are included in this special issue, have undergone rigorous peer review according to Algorithmica’s high standards. They include

  • An article by Gawrychowski and Uznański presenting an improved distance labeling scheme for unweighted planar graphs;

  • An article by Eppstein proving a new lower bound on parametric minimum spanning trees;

  • An article by Bercea and Even designing the first dynamic dictionary for multisets supporting constant-time operations with high probability;

  • An article by Sawada and Williams showing the first known construction of universal cycles for strings with fixed-content.

We would like to thank the authors for contributing their manuscripts, the referees for thoroughly reviewing these articles and the WADS 2021 program committee for helping with the selection of these articles. We also gratefully acknowledge the support of the WADS 2021 sponsors: Elsevier, Springer, the Faculty of Computer Science at Dalhousie University, the Atlantic Association for Research in the Mathematical Sciences (AARMS), the Fields Institute for Research in Mathematical Sciences, and the Pacific Institute for the Mathematical Sciences (PIMS).