A Masonic lodge (also called Freemasons' lodge, or private lodge or constituent lodge) is the basic organisational unit of Freemasonry.

It is also a commonly used term for a building where Freemasons meet and hold their meetings. Every new lodge must be warranted or chartered by a Grand Lodge, but is subject to its direction only by enforcing the published constitution of the jurisdiction. By exception, the three surviving lodges that formed the world's first known grand lodge in London (now merged into the United Grand Lodge of England) have the unique privilege to operate as time immemorial, i.e., without such warrant; only one other lodge operates without a warrant – the Grand Stewards' Lodge in London, although it is not entitled to the "time immemorial" status.

A Freemason is generally entitled to visit any lodge in any jurisdiction (i.e., under any Grand Lodge) in amity (recognition of mutual status) with his own Grand Lodge. In some jurisdictions, this privilege is restricted to Master Masons (that is, Freemasons who have attained the Order's third degree). He is first usually required to check, and certify, the regularity of the relationship of the Lodge – and be able to satisfy that Lodge of his legality of membership. Freemasons gather together as a Lodge to confer (also known by the term "work") the three basic Degrees of Entered Apprentice, Fellowcraft, and Master Mason.

Freemasons meet as a lodge, not in a lodge. In this context, the word "lodge" refers to a local chapter of Freemasons, meeting as a body. However, the term is often misused to refer to the buildings or rooms that Masons meet in. Masonic premises are also sometimes referred to as Temples ("of Philosophy and the Arts"). In many countries Masonic centre or Masonic hall has now replaced these terms to avoid arousing prejudice and suspicion, or confusion with a religious building. Several different lodges, or other Masonic organizations, often use the same premises at different times.

Blue lodges, craft lodges or ancient craft lodges are those that work the first three Masonic degrees: Entered Apprentice, Fellowcraft, and Master Mason, rather than the appendant Masonic orders such as York Rite and Scottish Rite. The term "craft lodge" is used in Great Britain. The Blue lodge is said to refer to the traditional colour of regalia in lodges derived from English or Irish Freemasonry. Although the term was originally frowned upon, it has gained widespread and mainstream usage in America in recent times.

Research lodges have the purpose of furthering Masonic scholarship. Quatuor Coronati Lodge, in London, is an example of a research lodge; it has a strictly limited membership and receives visitors and papers from all over the world. Many jurisdictions have well-established research lodges, which usually meet less frequently than blue lodges and do not confer degrees.

In Great Britain, a lodge of instruction (LOI) may be associated with a Lodge, but is not constituted separately. The lodge of instruction provides the officers and those who wish to become officers an opportunity to rehearse ritual under the guidance of an experienced brother; there may also be lectures around the ritual and the symbolism in the lodge within a Lodge of Instruction, in order to develop the knowledge and understanding of the membership.

In some jurisdictions in the United States, the lodge of instruction serves as a warranted lodge for candidate instruction in other aspects of Freemasonry besides ritual rehearsal, as well as hosting a speaker on topics both Masonic and non-Masonic.