Affinity materials are valuable resources in various biotechnological and biosensing applications due to their exclusive benefits, including cost-effectiveness, structural stability, diversity, and multi-functionality. These materials are designed to exhibit high selectivity toward specific target molecules, termed analytes, playing an essential role in a wide range of molecular recognition processes. However, different biorecognition elements possess unique properties, necessitating a comprehensive understanding of their advantages and disadvantages for successful molecular biosensor development. These recognition elements encompass natural biomolecules, like antibodies and enzymes, semi-synthetic ones, viz. nucleic acids and peptides, and fully synthetic molecules, such as aptamers and molecularly imprinted polymers (MIPs). This chapter aims to explore the fundamentals of molecular recognition, discusses different types of recognition elements—known as molecular receptors—elucidates their structure, and highlights their involvement in various applications. By providing a comprehensive overview of affinity receptors, this chapter enables scientists from different backgrounds to gain a meaningful perspective into the scientific domains related to affinity materials.