The road to Friday's ruling has been long and winding, partly because each state establishes its own marriage laws. States did not explicitly allow or ban same-sex marriage until 1973, when Maryland added a line to its Family Law Code stating that "only a marriage between a man and a woman is valid in this State."
Others followed suit, and couples sporadically contested some of the rules for many years. Then in 1996, President Bill Clinton signed the Defense of Marriage Act, which prohibited federal recognition of same-sex marriages.
DOMA, as that law was known, had myriad implications for same-sex couples, but one of the more frustrating involved taxes. When one spouse died in an opposite-sex marriage, the other could inherit their assets tax-free, thanks to the marital deduction—but same-sex couples did not have that benefit. In addition, same-sex couples had to file their federal tax returns separately, which was more cumbersome and often meant they had to pay more in taxes and accountants' fees. They also had to remember to carry their marriage license and other documents with them when they crossed state lines.
DOMA remained on the books even as various states and communities passed laws allowing either civil unions or same-sex marriages. The first legally recognized same-sex marriage took place 11 years ago, and the Supreme Court struck down DOMA exactly two years ago, on June 26, 2013, with a decision that stated, in part, that DOMA led to "deprivation of the equal liberty of persons that is protected by the Fifth Amendment."
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That ruling allowed same-sex couples to file joint federal tax returns, but left them having to file separately in states that did not recognize their marriage.
It also left important uncertainties about same-sex marriage, notably whether states that did not recognize those unions were required to recognize marriages that took place in other states, and whether states themselves have the right to ban same-sex marriage.
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The case before the Court, Obergefell v. Hodges, was consolidated with several others. In the original Obergefell suit, James Obergefell, an Ohio resident, married his longtime partner John Arthur when Arthur was dying from ALS. Because Ohio does not recognize same-sex marriage, they flew to Maryland and were married on an airport tarmac. Obergefell sued after Arthur died and Ohio would not list him on the death certificate.
Tim Bresnahan, head of Northern Trust's national LGBT and nontraditional families practice, said the ruling will have very different implications for same-sex couples depending on their circumstances. Those already married in states that were recognizing same-sex marriage may not feel much difference, he said. Married couples in states that were not recognizing same-sex marriage will see important benefits when it comes to estate taxes and the like. Even long term couples that do not plan to marry may see changes, he said.
It will be extremely important for couples to obtain advice from financial advisors, accountants, or lawyers, Bresnahan said, since each state has different tax and inheritance laws. For example, in Texas, which did not recognize same-sex marriage, the homestead law holds that when one spouse dies, the surviving spouse automatically has the right to remain in the home. That would not have applied to a same-sex couple before Friday's ruling.
"Same-sex marriage at the state level have only been valid for 11 years, so this area of law is still new," he said.
Friday's ruling may be a landmark one, but even so, same-sex couples may face hurdles, Armstrong said. Localities may still challenge some of the provisions.
"There are still things people are going to have to do," Armstrong said. "You still have to carry travel documents—your marriage certificate, your durable power of attorney, your health-care proxy. Frankly, I would do this even with marriage equality. Couples may still face resistance.
"My husband and I have been together for a number of years and have been together for a number of years before we got married, and then the Supreme Court ruled on [the DOMA case] and it really made a difference for us," said Armstrong. "Many states don't have job discrimination laws and housing protection, but to know we don't have to be thinking about all these workaround strategies and worrying about what state do we move to—it's hugely important, hugely symbolic."
—CNBC's Tom Anderson contributed to this report.
UPDATED: This story was updated to include remarks from Tim Bresnahan, head of Northern Trust's national LGBT and nontraditional families practice.