Guanidine-based functional groups occur in many branches of chemistry, due in part to their ability to exist as neutral (guanidine), cationic (guanidinium), and anionic (guanidinate) entities. With such a rich chemistry, it is undoubtedly difficult for researchers to follow the development of so many aspects of guanidine chemistry, especially when results are published in a wide spectrum of journals. Thus, it is timely that we use this specialissueoftheAustralianJournalofChemistrytotakestock and bring together a selection of the diverse research derived from these functionalities. We hope that through this collection we will help to cross-pollinate ideas and generate renewed