New York has legalized recreational marijuana, after years of failed attempts and stalled efforts.

State lawmakers approved a bill on Tuesday that legalizes the drug for adults 21 and older and moves toward the creation of a potential $4.2 billion industry that could become one of the nation’s largest markets. Gov. Andrew M. Cuomo signed the bill into law on Wednesday.

Is recreational marijuana legal in New York?

Using it is now legal. Selling it will be legal too, once regulations are in place.

What does legalization mean for New Yorkers?

New Yorkers are now allowed to possess up to three ounces of cannabis for recreational use or 24 grams of concentrated cannabis, such as oils derived from a cannabis plant.

People who are 21 and older are allowed to use, smoke, ingest or consume cannabis products; they can also give them to others who meet the same age requirement.

At home, people will be permitted to store up to five pounds of cannabis, but they will have to take “reasonable steps” to make sure it is stored in a secure place.

There are penalties, ranging from a simple violation to a felony, for possessing more than the permitted amount of cannabis and for selling the drug without a license.

Where is marijuana allowed?

Liz Krueger, the bill’s sponsor in the Senate, said people are legally allowed to smoke in public wherever smoking tobacco is legal. “As far as right now, the law passing today, if you can smoke tobacco there, you could smoke marijuana there,” she said on Tuesday.

Smoking cannabis is not permitted in schools, workplaces or inside a car.

Ms. Krueger said localities, as well as a new state cannabis agency, could create rules to more strictly regulate smoking cannabis in public. Smoking publicly where it’s not permitted will subject people to a civil penalty of $25 or up to 20 hours of community service.

An officer, however, is not allowed to use the smell of cannabis as a justification to stop and search a pedestrian.

People are legally allowed to smoke cannabis in private residences, as long as the landlord doesn’t prohibit you from doing so, as well as in hotels and motels that permit it.

Club-like lounges or “consumption sites” where cannabis — but not alcohol — can be consumed will also be permitted in several months, when regulations are in place. Municipalities could opt out of allowing these sites.

How can I buy it?

The law creates retail licenses, paving the way for brick-and-mortar dispensaries where people can purchase cannabis products. Localities can opt out of allowing dispensaries and will have until the end of the year to do so.

Consumption at dispensaries will be limited to businesses that have an on-site consumption license.

The state will also issue licenses for the creation of cannabis delivery businesses, which means people will be able to get the drug delivered to their homes, something localities would not be able to block.

What about impaired driving?

It remains illegal to drive under the influence of marijuana, just as it’s illegal to drive while intoxicated by alcohol, and the police will still be able to pull people over who they believed were impaired.

An officer can use the smell of burned cannabis as a reason to suspect that a driver is under the influence, but he or she is only allowed to search parts of the car that are readily accessible to the driver, so not the trunk, for example.

Unlike with alcohol, there is currently no easy way to quickly and reliably measure whether a person is under the influence of cannabis, especially since traces of the drug can stay in someone’s system after the high has worn off.

So under the new law, the Health Department will be required to look at emerging devices that could potentially allow officers to use a saliva test to detect whether a driver is high.

What will change for medical marijuana patients?

The state’s existing medical marijuana program, first legalized in 2014, will undergo several changes aimed at making it less restrictive.

The list of medical conditions covered will be significantly widened and will include Alzheimer’s disease and muscular dystrophy. Patients will no longer be restricted from smoking medical marijuana, and the current 30-day cap on supply for patients will also be doubled.

Medical marijuana companies will be allowed to enter the more lucrative recreational market under certain circumstances, a measure they aggressively lobbied for.

Will it be legal to grow marijuana at home?

Yes. For recreational purposes, users will be allowed to cultivate up to six plants at home, indoors or outdoors, and a maximum of twelve plants total per household. They will not be allowed to do so, however, until 18 months after the first adult-use dispensary opens.

Medical marijuana patients, or their designated caregivers, will also be able to grow the plants, six months from now.

When would legal marijuana sales begin?

The timeline for dispensaries to open and sales to kick off remains distant. The law doesn’t provide a specific timeline, but the first sales aren’t expected until at least 2022.

Officials must first determine how the industry will operate, from the regulation and taxation of sales to the allocation of licenses for cultivators, processors, wholesalers, retailers and delivery services.

A new state Office of Cannabis Management and Cannabis Control Board will craft and oversee the new regulations.

What disparities is this law designed to correct?

One 2018 analysis by The New York Times found that Hispanic people across New York City had been arrested on low-level marijuana charges at five times the rates of white people in recent years.

The imbalance was even starker for Black people, who in Manhattan were arrested at 15 times the rate of white people.

But surveys have shown that Black and white people use marijuana at similar rates. And in neighborhoods where people called to make complaints about marijuana at similar rates, arrests were almost always made at a higher rate in the area with more Black residents.

Officials hope the new law will help put an end to those disparities.

Millions of dollars in tax revenue from sales will be reinvested each year in communities affected by racially disproportionate policing on drugs. A significant amount would also be steered to fund public education and drug prevention treatment.

A sizable portion of business licenses would be reserved for minority business owners, disabled veterans and distressed farmers, among others.

What happens to those with marijuana convictions?

People with certain marijuana-related convictions for activity that is no longer criminalized will have their records automatically expunged.

There is some precedent for such a move: In 2019, more than 150,000 people with some low-level marijuana convictions in New York had them cleared from their records.

Why did this take so long?

Mr. Cuomo and Democrats in the State Legislature tried several times to legalize marijuana in recent years. But each time, efforts unraveled.

In 2019, for example, the plan for legalization collapsed as disagreements over how to regulate the industry and how revenue dollars should be controlled, along with hesitation from moderate lawmakers, could not be overcome.

Mr. Cuomo vowed last January — and again this year — to finally push the bill over the line.

The efforts recently gained momentum, however, when they received a boost amid Mr. Cuomo’s recent scandals. Striking a deal for legalization became a higher priority for the governor, several lawmakers and lobbyists believe, as he sought to shift attention away from his compounding crises.

The new dynamic prompted Mr. Cuomo’s team to concede on many issues they had previously held the line on, such as how the tax revenue would be distributed, leading to a deal that more closely reflected Democratic lawmakers’ wishes.

What about other states?

More than a dozen other states and Washington, D.C., have taken similar steps.

In New Jersey, Gov. Philip D. Murphy signed into law three bills last month that permit and regulate the use of recreational marijuana. It became the most populous state in the Northeast to opt for legalization.

Penalties for underage possession were also eased, with written warnings and referrals to community services instead of harsh fines or criminal punishments.

Legal sales in New Jersey, however, remain at least several months away.