Blue Bloods is a police procedural/drama series on CBS, filmed on location in New York City. The show premiered on September 24, 2010, with episodes airing on Fridays at 10:00 pm.

The series follows the Irish-American Reagan family of police officers with the New York City Police Department (NYPD). Francis "Frank" Reagan (Tom Selleck) is the Police Commissioner. He was a U.S. Marine Corps officer and a Vietnam veteran before he joined the NYPD. He is a widower whose son Joe died in the line of duty, leaving him three remaining adult children—Danny, Erin, and Jamie.

Danny (Donnie Wahlberg) is a top NYPD detective, holding the rank of Detective First Grade, but is sometimes hard-nosed and does not always go by the book. Danny is also a Marine veteran, having served as in the Iraq War. Danny's partner at the beginning of the series is Detective First Grade Jackie Curatola (Jennifer Esposito); however, in the beginning of season 3 Kate Lansing (Megan Ketch) became an interim partner. By Episode 13 of the show's 3rd season, Danny Reagan obtains his 3rd new partner, Candice McElroy (Megan Boone).

Erin (Bridget Moynahan) is an assistant district attorney in Manhattan who prosecutes many of the criminals Danny arrests.

Jamie (Will Estes), Frank's youngest child, is a recent graduate of Harvard Law School and is a rookie officer on the police force after graduating from the police academy.

Henry (Len Cariou) is Frank's father, former NYPD officer and also a former NYPD police commissioner, now retired. Henry served in the United States Marine Corps during the Korean War. Henry often provides advice to his son and grandchildren.

The family is close-knit; each episode includes a scene wherein they all have dinner together with their spouses and children and discuss their current cases.

Frank's middle son, Joseph, was an NYPD police detective who died in the line of duty. Joe was involved with the Federal Bureau of Investigation (FBI) investigating a group of dirty cops, who were operating within a fraternal organization called the "Blue Templar". Joe was murdered by these dirty cops when his covert investigation into their corruption was getting too close.

A running thread through the first season is Jamie's picking up Joe's investigation. The FBI tried to recruit Jamie, but he instead conducted his own covert investigation into Joe's death. Joe's murderers try to kill Jamie by tampering with the brakes on his car, but fail. Jamie then informs his father Frank, his brother Danny, and his grandfather Henry about his suspicions after the attempt on his life.

Along with Erin, they join together and complete Joe's investigation of the Blue Templar. After gathering sufficient evidence to obtain arrest warrants, Frank leads a team of police officers, including Danny and Jamie, and they arrest all the corrupt cops at a covert meeting while the dirty cops are dividing up stolen drug money. A detective named Sonny Malevsky (Michael T. Weiss), who was leading the gang of dirty cops, admits to killing Joe, but Malevsky commits suicide with his own service pistol after confessing to the murder.

Jamie was engaged to Sydney (Dylan Moore), a fellow Harvard graduate who broke off their engagement after he became obsessed with investigating Joe's murder.

Erin is divorced and has one teenage daughter, Nicki (Sami Gayle).

Danny is married to Linda, a nurse, with two children, Jack and Seán.

Jamie's field training officer is Sergeant Anthony Renzulli (Nicholas Turturro), who is tough but fair with Jamie and thinks Jamie has what it takes to be a great cop.

Main cast:

Tom Selleck as Francis "Frank" Reagan, the Police Commissioner of New York City and widowed father of Danny, Erin, and Jamie. His second son, Joe, was killed in the line of duty May 15, 2009 (15 months before the beginning of the series). Frank was a Marine officer during the Vietnam War and often serves as the moral center of the family. He has an indifferent attitude towards politics, often taking on the mayor and numerous reporters who misinterpret his actions. He tries hard not to judge people, and tends to purse his lips together when hearing bad news or the horrific details of an ongoing case. His wife Mary died September 14, 2005. The death of his wife, son, mother and the thousands who perished on 9/11 weigh heavily on him, and the person who is best at lifting his spirits is his father, who often talks to him late at night when he cannot sleep. Frank is a devout Catholic and has good relationships with his local church and his city's archdiocese, to whom he talks about personal and police matters. Frank lives in the Bay Ridge section of Brooklyn along with his father.

Donnie Wahlberg as Det. Daniel "Danny" Reagan. Danny was a Marine in Gulf War II. He is happily married with two sons and lives with his family in Staten Island. He is old-school; his hotheadedness and harsh methods of detective work sometimes gets him in trouble, which his father worries about. Although he violates police procedure from time to time, he is hard on other policemen when he feels they are unprofessional or not doing their duty to its utmost.

Bridget Moynahan as Erin Reagan-Boyle, Assistant District Attorney and single mother. Erin is almost raped and killed at the end of season 1, episode 9 ("Re-Do"), though Frank saves her life by shooting her attacker dead. She is mostly by-the-book in matters of criminal justice, often to the annoyance of Danny and her grandfather. As of season 2, episode 9 ("Moonlighting"), she is 36 years old, but in season 3, episode 17 ("Protest Too Much"), it is mentioned that she recently celebrated her 40th birthday. In "Ends and Means" (season 3, episode 20) Erin is promoted from senior counsel to deputy Trial Bureau chief.

Will Estes as Jamison "Jamie" Reagan, a younger police officer and recent Harvard Law graduate. Like his father, he is mostly silent on his political beliefs. He was the one who continued Joe Reagan's investigation into the Blue Templar in Season 1. In Season 2, he takes advantage of a chance opportunity to go undercover in the Sanfino crime family. He is stationed at the 12th Precinct.

Len Cariou as Henry Reagan, retired Police Commissioner, father of Frank (grandfather of Danny, Erin, and Jamie; great-grandfather of Nikki, Sean, and Jack). His childhood during the 1920s and 1930s was hard due to his father's alcoholism and inability to hold a job. Henry was a Marine in World War II and Korea, and joined the NYPD in 1952. Like his grandson Danny, Henry is socially conservative and hates the political correctness of modern law and order. His wife Betty died December 2, 2001. Cariou, separated in age from Selleck by only six years, wears make-up and a dental prosthetic for the part of Henry.

Amy Carlson as Linda Reagan, wife of Danny and mother of their two sons. She loves her husband and the Reagan family, but at times Danny's obsessive attitude toward collaring criminals makes her wonder whether he views his job as a higher priority than his family. In seasons 1 and 2, she was a stay-at-home mom, but she returns to her nursing job in season 3.

Sami Gayle as Nicole "Nicki" Reagan-Boyle, Erin's daughter and an aspiring cop. As of season 3, episode 3 ("Old Wounds") she is 16 years old. She is a very curious young girl and is not afraid to question her uncle Danny and great-grandfather about police matters, as well as challenging their old school conservatism. In the pilot episode, Nicki is portrayed by actress Marlene Lawston.