Hydrogels are soft solids that consist mainly of water. Low molecular weight gelators are small molecules that self-assemble in solution to form long fibres. These fibres can entangle and cross link, forming a network and trapping the solution to form a self-supporting gel matrix. Gels formed using low molecular weight gelators are generally reversible, for example, they melt and then re-form on a heat–cool cycle. Other triggers for self-assembly include changes in pH, the addition of salts or specific enzymes. There are a wide variety of molecules that can be used as gelators, which means that gels with different functionalities and responses can be prepared. This means that gels can be tailored to specific needs. Here, we discuss the different types of molecule that can be used, the different triggers and show how these gelators can be used to prepare useful materials for applications such as cell culture, drug delivery, and sensors.