Cyclization and annulation reactions initiated by ring-opening of small rings, especially cyclopropanes and cyclobutanes are now well-established in synthetic chemistry. Nevertheless, the potential of aminocyclopropanes and cyclobutanes, an important subclass for the synthesis of nitrogen-rich building blocks, has remained unexploited for a long time, despite important pioneering results. In the last decade, the situation has changed dramatically and new catalytic methods have emerged both for cyclization and annulation reactions. The purpose of this feature article is to present recent progress in this area, including our own work using donor-acceptor cyclopropanes and cyclobutanes.