In this chapter, we consider annuities. An annuity is a sequence of payments, usually equal, made at equal intervals of time. An example of an annuity is a home mortgage which is paid monthly. The focus of this chapter is on simple annuities. A simple annuity is an annuity for which the payment interval and interest conversion period coincide, that is, the interest is compounded at the same frequency as the payments are made. An accumulated value or a future value of an annuity is the equivalent dated value of all payments due, at the end of the term. A discounted value or a present value of an annuity is the equivalent dated value of all payments due, at the beginning of the term. We derive the formulas for accumulated and discounted value of both ordinary annuity and annuity due, where ordinary annuity is an annuity for which periodic payments are made at the ends of payment intervals, while annuity due is an annuity for which periodic payments are made at the beginning of payment intervals.