Equal protection analysis begins by identifying the classification, because the level of scrutiny that follows is nearly determinative.
Strict scrutiny applies to classifications based on race, national origin and alienage in most contexts, and to those burdening fundamental rights. The law must be narrowly tailored to a compelling government interest. Few survive.
Intermediate scrutiny applies to sex-based classifications and to illegitimacy. The classification must be substantially related to an important government interest, and for sex-based classifications the justification must be exceedingly persuasive and not rest on overbroad generalisations.
Rational basis applies to everything else, including economic and social regulation. The classification is upheld if rationally related to a legitimate interest, and the government need not have articulated the reason at the time.
Rational basis with bite. Some decisions have invalidated classifications under a nominally deferential standard where the record suggested animus toward a group.
Discriminatory purpose. A facially neutral law is subject to heightened review only on proof of discriminatory purpose, shown through impact, historical background, departures from normal procedure and legislative history.
Class of one. A claim that an individual was singled out without rational basis is recognised, though not in public employment, and is frequently pleaded in land use and code enforcement disputes.