A flexible labor market is one in which it is easy and inexpensive for firms to vary the amount of labor they use, including by changing the hours worked by each employee and by changing the number of employees. This often means minimal regulation of the terms of employment (no minimum wage, say) and weak (or no) trade unions. Such flexibility is characterized by its opponents as giving firms all the power, allowing them to fire employees at a moment’s notice and leaving workers feeling insecure. Opponents of labor market flexibility claim that labor laws that make workers feel more secure encourage employees to invest in acquiring skills that enable them to do their current job better but that could not be taken with them to another firm if they were let go. Supporters claim that it improves economic efficiency by leaving it to market forces to decide the terms of employment. Broadly speaking, the evidence is that greater flexibility is associated with lower rates of unemployment and higher GDP per head.