兼职，又称计时人员，是一种劳工的类型，意指有全职者或学生于工余或课余时间另找一份或多份工作，而一边读书一边兼职的学生在**称为工读生，在中国大陆称为勤工俭学，香港称为半工读或半工半读。一般店家在征求兼职时，不一定会限制其身份一定得是学生，所以工读生和一般计时人员之间其实没有什么差别。

另外，一些人于工余或课余时间以自雇方式工作，亦是兼职的一种形式。这类兼职常见的有上门补习导师（家庭教师）、电脑维修、编程、钟点家务助理、业余模特儿等。

一般而言，兼职的工作时间会少于正常工时的职员，且工资亦较正职人员略低。依工作性质的不同，工时和工资不一定会比正职人员来得低，一般来说，持续性、定期的兼职工时一般较长，工资亦较低，而短期、临时或非定期的兼职则工资较高。

A part-time contract is a form of employment that carries fewer hours per week than a full-time job. They work in shifts but remain on call while off duty and during annual leave. The shifts are often rotational. Workers are considered to be part-time if they commonly work fewer than 30 or 35 hours per week. According to the International Labour Organization, the number of part-time workers has increased from one-fourth to a half in the past 20 years in most developed countries, excluding the United States. There are many reasons for working part-time, including the desire to do so, having one's hours cut back by an employer and being unable to find a full-time job. The International Labour Organisation Convention 175 requires that part-time workers be treated no less favourably than full-time workers.