The legal situation surrounding abortion rights is very heterogenous (different) across legal systems and the regime under which abortions are performed varies greatly by country. In many states, including some in the European Union, abortion is illegal except under narrow circumstances. Others are more liberal and allow abortion under a wider set of conditions. In the United States, abortion has been governed by a trio of Supreme Court decisions, which are discussed below. In general, most abortion laws include either one of a combination of the following criteria:

• Trimester regime or viability: Many legal systems allow abortion based on the timeline of the pregnancy and how far along it is. The earlier in the pregnancy, the easier the abortion. The longer the pregnancy has been carried out, the more difficult abortion becomes. This represents a gradual shift in the protection of interests. Early on in the pregnancy, the mother's right to choose outweighs the fetus' right to life, whereas later in the pregnancy when the fetus is more developed and gets closer to being viable (able to live on its own), the fetus' right t life outweighs the mother's right to chose. 

• Healthcare provider or hospital: In many states, the right to get an abortion is made conditional on the requirement that the abortion must be carried out by a doctor or other healthcare provider, or that it must be performed in a hospital setting. This creates the problem that many rural areas are seriously disadvantaged when it comes to access to abortion, simply because there are no hospitals in a several hundred mile radius or because there are no healthcare providers at a reasonable distance willing to perform the procedure. 

• Counseling: Many countries also make the access to abortion contingent on a mandatory counseling session with a social worker or psychologist on staff at the abortion center. Such counseling sessions can include a variety of topics, such as a discussion of the medical basis for abortion, its irreversibility, its possible psychological effects, the fetus' prenatal development (gestation) and ability to feel pain (conservative estimates between 12-18 weeks of gestation, possibly later).

• Waiting period: In addition to mandatory counseling, many systems also require a mandatory waiting period between the counseling and the abortion (typically at least 24 hours, but can be up to several days in some countries). This in effect often requires two separate trips to the abortion facility, which in some regions can be a serious impediment to the logistical organization of getting an abortion.

• Medical reasoning: It is also not untypical for legislators to make the legality of an abortion contingent on medical reasons (this is for instance the situation in the UK). Such medical considerations include the question whether the pregnancy would pose a treat to the life, or the physical or mental health of the mother (in the UK over 90% of abortions fall under the mental health category), whether another child would pose an existential financial threat to the family (including the livelihood of already existing children), or whether the fetus is likely to suffer from genetic disorders or other severe mental or physical disability.

• Funding: Often there are also specific limitations on the funding for abortions regulated in such legislations (such as no public funds may be used or private funding only if an extra premium applies). This significantly restricts the access to abortion, especially in indigent communities, where it is often most needed (for instance because young or poor mothers often do not have the funds to travel across state lines to obtain it). 

• Parental consent: It is not uncommon for many states to prohibit abortions sought by minors if one or both parents do not consent.