An individual mandate is a requirement by law for certain persons to purchase or otherwise obtain a good or service.
The Militia Acts of 1792, based on the Constitution's militia clause (in addition to its affirmative authorization to raise an army and a navy), would have required every "free able-bodied white male citizen" between the ages of 18 and 45, with a few occupational exceptions, to "provide himself" a weapon and ammunition. (See Conscription.)
The Militia Acts were never federally enforced, so their constitutionality was never litigated.
An Act for the relief of sick and disabled seamen, signed into law by President John Adams in 1798, required employers to withhold 20 cents per month from each seaman's pay and turn it over to a Collector of the Federal Treasury when in port, and authorized the President to use the money to pay for "the temporary relief and maintenance of sick or disabled seamen," and to build hospitals to accommodate sick and disabled seamen.
In 2012, Eliot Spitzer credited what he called "spectacular historical reporting by Professor Einer Elhauge," who was employed by the campaign to re-elect President Obama, for finding 18th century legislation that Spitzer and Elhauge called individual mandates. However, as it was similar to workers' compensation, Social Security Disability Insurance, and Medicare, there exists some debate as to whether it can be properly called an individual mandate, because it did not require anyone to purchase anything themselves.
In the United States, the Patient Protection and Affordable Care Act signed in 2010 imposed a health insurance mandate which took effect in 2014. Under this law insurance companies are restricted in their ability to alter insurance rates based on the current health of the individual buying the insurance. In effect this means healthier individuals will pay a higher rate and less-healthy individuals will pay a lower rate than they would if rates were based on how healthy they are. Healthier individuals will tend to opt out of the system. They tend to make fewer claims and their premiums are used to pay the claims of the less-healthy. The insurance companies will have to raise rates on those remaining insured in order to make up the lost revenue. That will further increase the pressure on healthier individuals to opt out of buying health insurance, which will further increase rates, until the market collapses. Mandated insurance is intended to prevent the downward spiral.