Many of the important distributions belong to a special class of distributions because their probability mass function (PMF) or probability density function (PDF) satisfies a specific mathematical structure. From the perspective of point estimation, this mathematical structure is useful for ease in finding estimators with important statistical properties. The mathematical structure of exponential families will also be useful in hypothesis testing, interval estimation, and asymptotic evaluations. Exponential families also satisfy what we will come to know as "regularity conditions."