Immediate Early Genes (IEGs) are the foremost genes to respond to any stimuli within the cell. This group of genes are in fact transcription factors which are associated with the growth, proliferation, differentiation and apoptosis of the cells. Fos proteins produced by c-fos gene, which is an IEG, and Jun proteins produced by c-jun gene, which is also an IEG, are the components of the transcription factor complex, namely the Activator Protein-1 (AP-1), and they act together. The members of the AP-1 complex modulate various gene expressions. All AP-1 proteins regulate certain aspects of the cellular responses to growth factors. These components are critically linked to many cellular processes including growth, proliferation, differentiation, apoptosis, and oncogenic transformation. Carcinogenesis resulting from the impairment in the cellular processes controlled by IEGs and AP-1 has been described. Besides the vital importance of their normal cellular expressions, the abnormal expressions of IEGs and AP-1 could cause serious problems such as oncogenic transformation. There are several ongoing studies about the substances and effectors causing overexpression or inhibition of AP-1. If the stages of oncogenic transformation and the role of AP-1 and IEGs in this transformation can be illuminated, carcinogenesis could be taken under control as well as some of the peculiarities of malignant cells could be beneficial for the treatments of various diseases.