Immediate early genes (IEGs) are a group of genes that are rapidly activated in response to various stimuli, such as growth factors, stress, or neuronal activity. They play a crucial role in cellular processes, including differentiation, survival, and synaptic plasticity. IEGs are often the first genes expressed after a stimulus, making them important for understanding how cells respond to changes in their environment. These genes typically do not require new protein synthesis for their expression, allowing for a quick response. Examples of immediate early genes include c-Fos, c-Jun, and Arc. Their study is significant in fields like neuroscience and cancer research, as they help elucidate mechanisms of cellular signaling and adaptation.