The objective of this chapter is to familiarize the readers with principles and practice of vaccinology. One should follow the National Vaccination Programs recommended for childhood and adults; also, there are institutional policies derived from the WHO and CDC’s ACIP, and these are periodically revised and updated. Good vaccination practices begin shortly after birth. Combination vaccines are necessary and important for the continuing success of our immunization program, especially when more vaccines are added to the already crowded immunization schedule. Adverse events of vaccines in general and specific to childhood immunizations and adult vaccinations are covered in this chapter. Travel vaccination includes polio vaccine, yellow fever vaccine, and typhoid vaccination. Vaccines for 65 years of age and older are pneumococcal vaccine, zoster vaccine, seasonal influenza vaccine, etc. Vaccination of transplant candidates and recipients is sometimes given little thought, especially when the urgency of transplant and the transplant workup takes precedence.