A 401k plan is a retirement savings plan that employers establish for their employees. You have to be employed to qualify for a 401k. Plans vary by employer and usually an employer will chose to work with one or more well known investment companies such as Fidelity, Nationwide or Vanguard but the responsibility for management of the plan rests with the employer. How much you will be allowed to contribute from your pretax earnings is fixed by the IRS and by the rules of the plan. How much you are able to contribute you have to work out for yourself. As an incentive to save for retirement your employer may also chose to match a percentage of your contributions into the plan but that is optional. 401k plans are not mandatory, employees chose either to participate or not to participate in the plan. 401k plans will also allow some flexibility in moving your funds between different types of investment strategies such as growth, value, income of for example emerging markets. 401k plans tend to be more conservative than other types of managed funds so the different investment strategies and flexibility in moving your funds between accounts are likely to be more restricted.