There are four types of conditional sentences in English: zero, first, second, and third conditional. The document provides examples and explanations of each type of conditional. The zero conditional describes always-true situations using the present simple tense. The first conditional speculates about possible present or future situations using if + present tense and will + bare infinitive. The second conditional speculates about unlikely present or future situations using if + past tense and would + bare infinitive. The third conditional always refers to the past using if + past perfect and would + perfect infinitive. Mixed and inverted conditionals are also discussed.