Ser and estar are the two verbs that mean "to be" in Spanish. Ser is used to describe characteristics or qualities that do not normally change, such as nationality, profession, or material composition. Estar is used to describe temporary conditions or locations. Some key differences in uses of ser and estar include telling time or dates (ser), expressing the present progressive (estar), describing origin or location (ser, estar), and impersonal expressions or possession (ser, estar). Knowing when to use ser versus estar is important as the meaning can change depending on which verb is chosen.