These Transactions publish archival papers in the broad area of Petri nets and other models of concurrency, ranging from theoretical work to tool support and industrial applications. ToPNoC issues are published as LNCS volumes, and hence are widely distributed and indexed. This Journal has its own Editorial Board which selects papers based on a rigorous two-stage refereeing process. ToPNoC contains: Revised versions of a selection of the best papers from workshops and tutorials at the annual Petri net conferences; Special sections/issues within particular subareas (similar to those published in the Advances in Petri Nets series); Other papers invited for publication in ToPNoC; Papers submitted directly to ToPNoC by their authors. The fourth volume of ToPNoC contains revised and extended versions of a selection of the best papers from the workshops held at the 30th International Conference on Application and Theory of Petri Nets and Other Models of Concurrency and from the 10th Workshop and Tutorial on Practical Use of Coloured Petri Nets and the CPN Tools. The nine papers provide good coverage of a diverse range of topics including workflow systems, model checking, agent-based software systems, the state explosion problem, structure theory for Petri nets, and modal logics. ‘The volume presents a good mixture of theory, tools, and practical applications related to concurrency and gives a useful snapshot of current research.