Falling in love with a television show is easy for most people. But falling in love with a television show that spans decades is like finding a needle in a haystack. And, with even more content out there than ever before, the odds of a television show lasting more than a few seasons is slim to none.

RELATED: 10 Best One Season TV Shows (According To IMDb), Ranked

However, there are a handful of primetime television shows that have managed to do the impossible and thrive for decades, sometimes even multiple decades. From crime and medical shows to TV classics and animated favorites, there doesn't seem to be any one type of show in particular that goes the distance, it all just depends on what happens to click with viewers. As a note, this list focuses specifically on network American television and doesn't include shows on cable or that originated in other countries.

Updated on May 2nd, 2021 by Kristen Palamara: With so many new shows and pilots being greenlit it's difficult for primetime shows to stand out amongst the lineup of new shows let alone run for dozens of seasons, but these shows have managed to do just that. These primetime TV shows have the most seasons and are the longest-running shows as each one of them aired new episodes for more than a decade and consistently kept enough of a fanbase to stay on the air for so long and still be successful up until the end.

Bonanza - 14 Seasons

Pa, Hoss, Adam, and Little Joe Cartwright share a laugh in the countryside in the TV show Bonanza.

Bonanza was a Western that first aired in 1959 and had its final episode in 1973 with over 400 episodes over its 14 seasons. The series followed a family of ranchers, Ben Cartwright and his 3 sons, trying to survive during and after the U.S. Civil War.

Fans tuned in every week for over a decade to watch the Cartwright family work on their land, called the Ponderosa, and live their more personal lives outside of work on the ranch as well.

Criminal Minds - 15 Seasons

Criminal Minds team JJ, Garcia, Prentiss, Rossi, Hotch, Reid, and Morgan.

Criminal Minds was an intriguing police procedural program with a twist as it focused on the FBI profiling team that used more psychological approaches to solving their crimes as they created a profile for people who might have committed heinous crimes and worked from there.

It was a gritty series that alleviated its serious moments with more comedic ones and had a large cast of characters with unique personalities. This balance made the series popular and kept it going for 15 seasons.

The Jack Benny Program - 15 Seasons

Two characters in a scene from The Jack Benny Program

The Jack Benny Program was similar to a sketch show as host and comedian Jack Benny would welcome new guests every week and provide laughs during their weekly primetime programming.

The series ran for over 300 episodes in its 15 seasons starting in 1932 and ending in 1965. Fans were obviously tuning in to the program with it lasting over 30 years on the air and one of the first weekly television programs for people to view at home.

ER - 15 Seasons

ER season 1 cast

ER was one of the first majorly popular medical dramas and paved the way for other series like Grey's Anatomy to be as popular as they are. ER ran for a total of 15 seasons and focused on several doctors, nurses, and other hospital employees working their jobs and living their lives outside of work.

Fans continued to tune into the show even as characters left and new characters were introduced and ER proved that the medical drama was a force to be reckoned with.

Supernatural - 15 Seasons

Supernatural Series Finale (Featured)

Supernatural ran for 15 years and 15 seasons on the CW as one of the channel's most popular and longest-running shows. The series followed the Winchester brothers, Sam and Dean, as they traveled the U.S., hunted monsters, and saved people.

Fans continued to tune into the series to see the character building of both the Winchester brothers and everyone they interacted with, human or supernatural creatures, including recurring fan-favorite character Castiel.

CSI: Crime Scene Investigation - 15 Seasons

Original cast of season 15 of CSI: Crime Scene Investigation - 15 Seasons

CBS's procedural forensics drama series CSI: Crime Scene Investigation premiered in October 2000 and ended its fifteen-year run in September 2015.

The series was so successful it helped launched a massively popular franchise which now includes three other television series, in addition to making the leap to video games and other forms of media. During its historic run, the series was nominated for various Emmys and other awards, earning it critical acclaim.

Grey's Anatomy - 16 Seasons

Season 16 cast of Grey's Anatomy dressed in their scrubs

Grey's Anatomy has dethroned ER as being the longest-running primetime medical drama series in September 2019 when the sixteenth season began airing on ABC.

The Shonda Rhimes-created drama first premiered in March of 2005 and since then has become a cultural phenomenon. Over the years there has been a revolving cast of characters— with several leaving over creative differences— but one thing that has remained the same is that the series promises to bring the drama every episode.

American Dad! - 17 Seasons

American Dad family hugging in front of their house

American Dad is one of two Seth MacFarlane-created animated series to earn a spot on the list of longest-running primetime television shows of all time. The series follows Stan Smith, a homeland security CIA agent, who must juggle his stressful job with his eccentric family which includes Roger, an alien who escaped Area 51.

American Dad first started airing on Fox in February of 2005 before moving to TBS in 2014 for the remaining six seasons. The series has since been renewed for two more seasons which will bring it to 19.

NCIS - 17 Seasons

NCIS CBS Season 16 actors all looking at the same thing

CBS's police procedural NCIS also makes the list of longest-running primetime television shows with seventeen current seasons and an eighteenth set to star premiering in the next few weeks.

RELATED: NCIS: 10 Major Ways Gibbs Has Changed Since Season 1

NCIS centers on Leroy Jethro Gibbs (Mark Harmon) and his team of Naval Criminal Investigative Service Special Agents as they investigate primes that deal with the Navy and Marine Corps. Like CSI, NCIS has created several successful spins off, turning it into a franchise.

Family Guy - 19 Seasons

The Griffens sitting around the TV looking shocked

Seth MacFarlane's longest-running animated show is none other than Family GuyThe animated sitcom first aired on Fox in January 1999 and has continued to call Fox home for the last nineteen seasons.

Family Guy is interesting because it was actually canceled by Fox after its third season. However, strong DVD sales and the success of reruns on Adult Swim inspired Fox to reverse its cancellation order. Since then, the series has continued to be a top performer for Fox and one that the network probably wouldn't be looking to cancel (again) anytime soon— though its future is somewhat uncertain given MacFarlane signing a deal with NBCUniversal earlier this year.

Lassie - 19 Seasons

Jeff and Lassie from the TV show Lassie

Throwing it way back, Lassie first premiered in September 1954 on CBS and continued to air there until March 1973 when the nineteenth and final season of the series wrapped.

Lassie's historical run is one that isn't talked about enough considering it consistently placed number one for CBS's ratings during its timeslot. One interesting thing to note is that the first two seasons of the series were produced in black and white before moving to color when the technology became more readily accessible, making it one of only a small number of shows that successfully straddled both eras of television.

Law & Order - 20 Seasons

Original cast of Law & Order

NBC's police procedural and legal drama Law & Order began airing in September of 1990 and completed its historic twenty-year run in May of 2010.

Like many procedurals, the series had a revolving ensemble cast that changed over time. In addition, the success of the series helped launched a sequel that is even more successful and longer-running than the original, something that very rarely happens with spin-offs.

Gunsmoke - 20 Seasons

Original cast of Gunsmoke - 20 Seasons

Another television classic that lasted nearly two full decades is the Western drama series GunsmokeThe series originated on CBS radio in 1952 and lasted in that format until 1961. However, during that time, a version also debuted on primetime on television in 1955 where it lasted twenty seasons before it ended in 1975.

RELATED: Top 10 Westerns Of The 21st Century According To IMDb

In addition to being the number 3 longest-running primetime television show of all time, Gunsmoke also holds the record for most episodes of a prime time, live-action, scripted television series with an astonishing 635 episodes aired.

Law & Order: Special Victims Unit - 21 Seasons

Original cast of Law & Order: SVU

Law & Order: Special Victims Unit premiered on NBC in September 1999 as a spin-off to the ever-popular police procedural and legal drama Law & Order. Like its predecessor, Law & Order: SVU has an ensemble cast and centers on legal and criminal cases, sometimes ripped from real-life headlines.

Since its premiere, the series has spanned 21 seasons and has been renewed through its 24th season. Despite being the second-longest-running primetime series of all time, Law & Order: SVU actually ranks fourth when it comes to overall episodes with 478 currently aired as TV seasons are much shorter now than they were even a couple of decades ago.

The Simpsons - 32 Seasons

The Simpson family sitting in their living room

Unsurprisingly, The Simpsons has earned the title of being the number one longest-running primetime television series of all time. Created by Matt Groening, The Simpsons began airing as a full-fledged half-hour show on Fox in December of 1989 after previously being just a series of shorts within The Tracey Ullman Show, and has since spanned a historic 32 seasons.

Since its inception, the series has earned 34 Primetime Emmy Awards and became Fox's first series to land a spot in the Nielsen's Top 30 ratings. In addition, the series has had a huge impact on American pop culture, becoming a "brand" of which the TV show itself is but a small part, especially in recent decades.

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