A bell tower is a tower that contains one or more bells, or that is designed to hold bells even if it has none. Such a tower commonly serves as part of a Christian church, and will contain church bells, but there are also many secular bell towers, often part of a municipal building, an educational establishment, or a tower built specifically to house a carillon. Church bell towers often incorporate clocks, and secular towers usually do, as a public service.

The term campanile (/ˌkæmpəˈniːli, -leɪ/ KAM-pə-NEE-lee, -⁠lay, US also /ˌkɑːm-/ KAHM-, Italian: [kampaˈniːle]), from Italian and deriving from campana "bell", is synonymous with bell tower; though, in English usage, campanile tends to be used to refer to a free standing bell tower. A bell tower may also in some traditions be called a belfry, though this term may also refer specifically to the substructure that houses the bells and the ringers rather than the complete tower.

The tallest free-standing bell tower in the world, 113.2 metres (371 ft) high, is the Mortegliano Bell Tower, in the Friuli-Venezia Giulia region, Italy.

Bells are rung from a tower to enable them to be heard at a distance. Church bells can signify the time for worshippers to go to church for a communal service, and can be an indication of the fixed times of daily Christian prayer, called the canonical hours, which number seven and are contained in breviaries. They are also rung on special occasions such as a wedding, or a funeral service. In some religious traditions they are used within the liturgy of the church service to signify to people that a particular part of the service has been reached.

A bell tower may have a single bell, or a collection of bells which are tuned to a common scale. They may be stationary and chimed, rung randomly by swinging through a small arc, or swung through a full circle to enable the high degree of control of English change ringing. They may house a carillon or chimes, in which the bells are sounded by hammers connected via cables to a keyboard. These can be found in many churches and secular buildings in Europe and America including college and university campuses.

A variety of electronic devices exist to simulate the sound of bells, but any substantial tower in which a considerable sum of money has been invested will generally have a real set of bells.

Some churches have an exconjuratory in the bell tower, a space where ceremonies were conducted to ward off weather-related calamities, like storms and excessive rain. The main bell tower of the Cathedral of Murcia has four.

In Christianity, many churches ring their church bells from belltowers three times a day, at 9 am, 12 pm and 3 pm to summon the Christian faithful to recite the Lord's Prayer; the injunction to pray the Lord's prayer thrice daily was given in Didache 8, 2 f., which, in turn, was influenced by the Jewish practice of praying thrice daily found in the Old Testament, specifically in Psalm 55:17, which suggests "evening and morning and at noon", and Daniel 6:10, in which the prophet Daniel prays thrice a day. The early Christians thus came to pray the Lord's Prayer at 9 am, 12 pm and 3 pm; as such, in Christianity, many Lutheran and Anglican churches ring their church bells from belltowers three times a day: in the morning, at noon and in the evening calling Christians to recite the Lord's Prayer. Many Catholic Christian churches ring their bells thrice a day, at 6 a.m., noon, and 6 p.m., to call the faithful to recite the Angelus, a prayer recited in honour of the Incarnation of God. Oriental Orthodox Christians, such as Copts and Indians, use a breviary such as the Agpeya and Shehimo to pray the canonical hours seven times a day while facing in the eastward direction; church bells are tolled, especially in monasteries, to mark these seven fixed prayer times (cf. Psalm 119:164).