This collection contains eight articles which are based on extended abstracts presented at the 30th International Workshop on Combinatorial Algorithms (IWOCA), which was held at the University of Pisa, Italy, from 23 to 25 July, 2019. These extended abstracts were among the top papers presented at IWOCA 2019, and were selected with a very competitive peer-review process after which only 36 papers out of 73 submissions were accepted. Out of these 36, 11 were invited to this special issue, and 8 of them have been accepted for publication. Compared with the original conference submissions, the articles have been extended by full proofs and additional results, and have undergone a further rigorous reviewing process, following the TOCS standard.