With diminishing success in drug development, manufacturers have been exploring new ways of making drug manufacturing process successful. Biomarkers play a crucial role in drug development (Bleavins, Carini, Jurima, & Rahbari, 2011). Pharmaceutical companies consider using biomarkers to increase the efficiency of new drugs. This paper explores biomarkers, their use, classifications and importance in drug development. Biomarker has various definitions from different groups. According to Biomarkers Definition Working Group, a it is defined as an indicator in pathogenic or biological processes, which can be measured and evaluated objectively in a given intervention in therapy (Bleavins et al., 2011). Clinical end point defines it as an indicator reflecting the feelings and functioning of a patient as well as his survival. Finally, surrogate endpoint defines biomarker, as an instrument whose intention is to substitute clinical end point (Bleavins et al., 2011). There are three types of biomarkers: type 0, I and II. Type 0 is an indicator in diseases and correlates with given symptoms. It is concerned with risks of a given exposure. Type I shows the effects or response of a given intervention or therapy in an organism during drug development. Type II biomarkers are surrogate indicators. This means that, change in a biomarker indicates clinical end (Bleavins et al., 2011). Biomarkers are used to measure the well-being of a person; both physical and mental. They are used to determine the state of an individual’s health (Zwierzina, 2008). In addition, they are used to measure the risks and influence of a given exposure, which can be as a result of environmental or hereditary factors. If a disease is caused by exposure to toxins, researchers may choose to measure the level of toxin concentration in an individual’s environment. Researchers can also measure the alleged toxin in food, water, air or soil directly. As a result, they are able to ascertain the risks and susceptibility associated with a given exposure (Zwierzina, 2008). Biomarkers are used to ascertain the severity of diseases. They can determine whether a disease is severe or not. Biomarkers are used to predict results. They are used in drug development; hence they can predict the efficacy of a new drug. In addition, they are used in determining the most efficient type of nutrition, intervention and treatment in a patient. Imaging a biomarker assists researchers to develop efficient drugs for a given disease; through evaluation of an individual and the response to the drug (Javitt Spencer, Thaker, Winterer, & Hajós, 2008). Post-therapy evaluation determines the efficiency of nutrition and intervention in an individual’s body. Biomarkers are used to evaluate a person’s response to therapy. Through biomarker imaging, the concentration of drugs in tissues can be measured (Javitt et al., 2008). In addition, receptor occupancy and characterization of receptors can be done to evaluate an individual’s response towards an intervention. Biomarkers are used to monitor compliance of a drug. They are supposed to meet the intended purpose and adhere to given regulations. To determine the compliance of a drug,