The following review provides a comprehensive summary of antimicrobial preservatives that are commonly used in licensed parenteral products to date. The information reviewed includes the general properties of the preservatives, the doses and frequency of their use, the classes of the preserved products (peptide, protein, vaccine, and small molecule products), the interactions with other formulation components, and the criteria commonly used for their selection in parental product formulations. It was revealed that phenol and benzyl alcohol are the two most common antimicrobial preservatives used in peptide and protein products, while phenoxyethanol is the most frequently used preservative in vaccines. Benzyl alcohol or a combination of methylparaben and propylparaben are generally found in small molecule parenteral formulations. The key criteria for antimicrobial preservative selection are the preservative's dose, antimicrobial functionality, and effect on the active ingredient. Additionally, the use of spectroscopic techniques (circular dicroism (CD) and fluorescence) and differential scanning calorimetry (DSC) were identified as common techniques used in evaluating an antimicrobial preservative for its impact on the conformational stability of peptide, protein, and vaccine antigens. The future use of preservatives is also discussed, including antimicrobial agents such as peptides, and regulatory requirements for antimicrobial effectiveness testing.