The main uses of the subjunctive include:

1. After the verb querer when there is a change of subject (but use the infinitive if there is no change of subject)

2. When one person tells (decir) or asks (pedir) another person to do something.

3. After expressions of emotion, such as esperar (to hope), sentir (to be sorry), temer (to fear), alegarse (to be glad), when there is a change of subject.

4. After dudar (to doubt) and other verbs expressing uncertainty.

5. After most impersonal expressions, such as es posible (it's possible), es importante (it's important), es necesario (it's necessary) if there is a subject for the subordinate verb.

6. In adjective clauses is the antecedent is indefinite

7. After certain conjunctions, such as para que (in order that), sin que (without), and antes que (before)

8. After time conjunctions, such as cuando (when), en cuanto (as soon as), hasta que (until), when futurity is implied.

9. In contrary-to-fact conditions, the past subjunctive must be used in the if-clause (and the main clause is in a conditional tense)