从属连词是连词的一种，用来引导名词性从句或状语从句。

连词通常引导一个从句，修饰主句。 由从属连词所引导的句子叫从句,而含有从句的句子叫作复合句·从属连词可分为三大类：

1、that （无词义，不做成分）if，whether （表达是否的意义，但不做句子成分）2、连接代词：who，whom，whose，what，which，whatever, whoever, whichever（有词义，在句子中可作主语、表语、宾语）3、连接副词：when，where，why，how，how many，how long，how far，however，whenever，wherever （有词义，作从句的状语）用法：从结构上说，英语连接词分两大类：并列连词和从属连词。并列连词连接两个或两个以上地位平等的字、词组或分句。例如：(1) Air and water are indispensable to me. (2) She likes going out with friends or playing outdoor games. (3) Most workers have a good income, so they look very happy. 从属连词连接两个或两个以上的分句，形成复杂句中的从属分句。例如： (4) He said that he did not want to go . (5) Many things have happened since I last saw him. (6) You may come if you want to. 从属连词用来连接各种从句。如动词是持续行动词，它要用肯定句，如：I studied hard until 12 o'clock last night.如果动词是瞬间截止性动词，则要用否定句，如:He didn't go to bed until his mother came back.由since,for,by,before, 来引导的时间状语从句。since 引导的时间状语是动作的开始时间，如:I have studied English since 1990.而by引导的时间状语通常是动作的结束时间，如：I had learned 25 English songs by the end of last term.·