Highlander: The Series is a science fantasy action-adventure television series featuring Duncan MacLeod (Adrian Paul) of the Scottish Clan MacLeod, as the eponymous "Highlander". It was co-produced by Rysher Distribution in the United States, Gaumont Television in France, Reteitalia in Italy, RTL Plus in Germany, and Amuse Video in Japan. An alternative sequel to the 1986 feature film Highlander, it features a storyline in which the protagonist of that film (Connor MacLeod, a member of a race of "Immortals") has not won "the Prize" sought by all Immortals, who still exist post-1985. Christopher Lambert reprised his role as Connor in the pilot episode, which introduced series protagonist Duncan MacLeod, an Immortal who was taken in by the same clan of Scottish Highlanders who had found and raised Connor generations before.

The series was an international hit and was nominated twice for the Motion Picture Sound Editors' Golden Reel Award (Foley Artist ("The Gathering"): 1992; Foley Artist ("The Darkness"): 1993), three times for the Gemini Award (Best Dramatic Series: 1996; Best Performance by an Actor in a Guest Role in a Dramatic Series: 1997 (John Pyper-Ferguson), 1996 (Bruce A. Young)), once for a Saturn Award (Best Genre Syndicated TV Series: 1997), and eight times for the Online Film & Television Association Award (Best Guest Actress in a Syndicated Series (Sandra Bernhard), Best Direction in a Syndicated Series, Best Writing in a Syndicated Series, Best Syndicated Series, Best Ensemble in a Syndicated Series: 1997; Best Actor in a Syndicated Series (Peter Wingfield), Best Syndicated Series, Best Ensemble in a Syndicated Series: 1998).

The pilot episode established the main character, Duncan MacLeod, and his girlfriend Tessa Noël (played by Alexandra Vandernoot), initially living quietly together as co-proprietors of the antique shop MacLeod & Noël Antiques. Richie Ryan (Stan Kirsch) was introduced as a thief breaking into their shop and witnessing the confrontation between Duncan, the evil Immortal Slan Quince (Richard Moll), and Duncan's fellow clansman Connor MacLeod, the central protagonist of the original Highlander movie franchise.

Also revealed was that Duncan had lived nearly 400 years, and was one of many such Immortals in the world. Connor had come to ask Duncan to return to the Game, to fight on the side of good against evil. "The Game" was the term used by the Immortals to describe their hunting of one another, seeking "Quickenings" by beheading their opponents. Duncan had been hiding from other Immortals for some time, removing himself from the Game. Now hunted by Quince, he had to face him, and by the end of the first episode, Slan was defeated and Duncan was clearly caught up in The Game again.

Storylines revolved around Duncan MacLeod and his relationships with mortals and other Immortals. Relationships formed a theme in the series, especially Duncan MacLeod's relationships with his friends, family, lovers, and foes (). As the series progressed, changes in concept become apparent, as well as normal growth in the characters and their relationships. Recurring Immortal characters such as Amanda and Methos made guest appearances in season one, and the Watchers, including Joe Dawson, were introduced in season two.

In the final episode of season 5, "Archangel", the character of Richie Ryan was killed off and the supernatural demon Ahriman introduced into the storyline. Of the 13 episodes of season six, two did not feature MacLeod, while in some he appeared in cameos: the producers were experimenting with introducing a new female Immortal character for a spin-off series. None of the introduced characters were chosen, and what came to be Highlander: The Raven featured the recurring character Amanda in a starring role. The spin-off series lasted for one season, consisting of 22 episodes.

Each episode began with an opening montage of scenes from Duncan's life, over which was a narration giving a brief overview of the series' theme. The first six episodes of the first season were narrated by Duncan himself:

I am Duncan MacLeod, born four hundred years ago in the Highlands of Scotland. I am Immortal and I am not alone. For centuries we have waited for the time of the Gathering, when the stroke of a sword and the fall of a head will release the power of the Quickening. In the end, there can be only one.