Drugs in the bloodstream are available in both free and bound forms in which the free drug is responsible for pharmacological activities. Since protein binding determines the amount of free concentration of the drug in the blood, determining the protein binding in the early stages of drug discovery and development is of great importance. Besides, it is most beneficial to measure the free concentration of a drug in personalized medicine and therapeutic drug monitoring. For this reason, the need for sensitive, selective, and fast analytical methods to measure the free concentration of drugs and their protein binding has increased. This review aims to summarize recent advancements in analytical approaches used for the determination of free drug concentration and plasma protein binding and will focus on the most important approaches used to determine plasma protein binding. Furthermore, the concepts of each method will be described and discussed, along with their inherent advantages and disadvantages.