Mitochondria are often referred to as ‘cellular powerhouses’ because of their role in ATP synthesis. In addition to their contribution to cell metabolism, mitochondria provide an essential storage site for intracellular Ca2+, are key to the regulation of apoptosis, form the site for haem, steroid and iron-sulphur protein synthesis, and are essential mediators of cellular redox sensing and signalling. Recent developments have highlighted additional roles for mitochondria in cellular signalling and immunity, and have established an important link between these organelles and autophagy. This issue's Minifocus showcases some of these mitochondrial functions and their regulation. On page 801 – in a Cell Science at a Glance article – Michael Murphy and colleagues provide an overview of mitochondrial redox signalling. In a second Cell Science at a Glance poster article (p. 795), Seok Min Jin and Richard Youle highlight the importance of the autophagic removal of damaged mitochondria (‘mitophagy’) and dissect the roles of the proteins PINK1 and Parkin in this process. In an accompanying Commentary (p. 807), Stephen Tait and Doug Green explore further the way in which mitochondria regulate autophagy. In addition, they summarise the roles that these organelles have as signalling platforms, transducers and effectors in the pathways regulating cell death and the innate immune response.