This chapter discusses: the uses of ser, the uses of estar, when serand estar are more or less interchangeable, estarused to mean ‘seem’, ‘taste’, etc., ser or estar used to change the meaning of adjectives. Ser is used with adjectives or adjectival phrases which indicate identity or nature, i.e. physical, moral and mental characteristics, as opposed to conditions or states. estar is used with adjectives and adjectival phrases that indicate mood, physical condition, temporary physical appearance or other non-characteristic features. Ser or estar both translate the English ‘to be’, but the difference between the two Spanish verbs is fundamental and sometimes subtle.