Adam-12 stars Martin Milner and Kent McCord, with several recurring co-stars, the most frequent being William Boyett and Gary Crosby.

The plots of most episodes follow Malloy and Reed as they handle the various calls for service that they are assigned to or come across, ranging from intense incidents such as pursuits, standoffs, shootouts, hostage-takings, gang violence, terrorism, and undercover assignments, to the mundane (and far more common) routine happenings like traffic stops, disputes, disturbances, narcotics crimes, DUI arrests, fights, and thefts.

At the start of the series, Malloy, seeking to resign after the death of his previous partner, is assigned to field train Reed, an inexperienced rookie.

Starting with the third season, the series was organized chronologically, and Reed completed his probationary period, with him and Malloy remaining partners.

The personal lives of Malloy and Reed came up on occasion and were often tied into their duties, though they rarely extended past conversations, episode subplots, or brief scenes.

Reed is married to a woman named Jean (played by several actresses, including Mikki Jamison and Kristin Nelson); in the second season, they are shown to have a son, Jim Jr. (or Jimmy).

"[12] The police vehicles used in the production of the show were purchased from local dealerships and outfitted by the prop department to accurate LAPD cruiser specifications.

[5] The driving scenes were filmed on public streets using a dedicated camera platform mounted to the cruiser's hood, which was towed by a station wagon.

Sides were added to create a large "black box" over the front of the vehicle with both ends "open", which allowed for more controlled filming circumstances.

The director and the sound man would sit in a rear-facing seat in the back of the station wagon towing the police car.

Starting with the third and fourth seasons, the series gradually shifted to filming in actual locations in Los Angeles and the San Fernando Valley.

Jo Ann Pflug, Mark Harmon, and Michael Warren were tested for their potential to replace Milner in episodes where McCord served as their training officer or partner.

Another idea proposed that the series be continued with Officer Ed Wells, played by Gary Crosby, replacing Malloy, who would be written off with a promotion to Sergeant at another division.

[17] Ronald Wayne Rodman pointed out that the theme of Adam-12 referred to a "military-style topic while portraying a sense of contemporary action".

[20] In 2003, the Los Angeles Police Department activated an actual unit with the 1-Adam-12 call sign, in service with the Central Division.

Milner and McCord made cameo appearances as their Adam-12 characters in several episodes of the fifth season of Rowan & Martin's Laugh-In, including one that parodied the series' in-cruiser dialogue scenes.

In the fourth OVA episode ("Revenge Road") of the 1987 anime Bubblegum Crisis, the call sign of an AD Police helicopter is "Adam-12".

[24] Episode 8, "Log 72: El Presidente", guest-stars James Sikking, later of Hill Street Blues fame (Lt. Howard Hunter), and other various character roles as an armed robber.

Episode 43, "Log 24: A Rare Occasion" stars David Cassidy of The Partridge Family as a neighbor of Reed's who falls victim to a drug pusher.

Episode 53, "Loan Sharks", guest-stars Eve McVeagh, film actress of High Noon, Tight Spot, and television series The Clear Horizon and Faraway Hill.

Episode 60, "Log 105, Elegy for a Pig" guest-stars Mark Goddard (Major Don West of Lost in Space) as Malloy's friend and police academy classmate, Officer Tom Porter; and shows a great deal of Malloy's backstory, as well as what happens when an LAPD officer is killed in the line of duty.

Episode 80, "The Million Dollar Buff",[29] guests-stars Lindsay Wagner (The Bionic Woman) as a jewelry counter attendant.

Episode 94, "The Tip", guest-stars Larry Linville (later of M*A*S*H fame as Frank Burns) as a police detective whom Malloy and Reed assist on an ongoing case.

Episode 97, "Mary Hong Loves Tommy Chen", guest-stars Foster Brooks, Keye Luke, and Jo Ann Worley.

Episode 98, "Sub-Station", guest-stars Frank Sinatra Jr., portrays a disturbed man who takes a stewardess hostage and demands a meeting with a Hollywood director.

Episode 103, "Dirt Duel", guest-stars Edd Byrnes of 77 Sunset Strip and Micky Dolenz of The Monkees as bikers.

Episode 105, "Airdrop", guest-stars singer Al Martino of The Godfather who portrayed "Paul Stocker", a drug smuggling private plane pilot.

Episode 131, "Venice Division", guest-stars Laurette Spang of the original Battlestar Galactica as a woman who fears for her life after receiving obscene phone calls.

In addition, Martin Milner's real-life son Andrew played Whitaker's stunt double in the minibike chase scene.

Episode 150, "Clinic on Eighteenth Street", guest-stars Sharon Gless, later of Cagney & Lacey fame and most recently co-star of Burn Notice on USA Network and Frank Sinatra Jr. in his third role on the show.