This is a list of the largest cosmic structures so far discovered. The unit of measurement used is the light-year (distance traveled by light in one Julian year; approximately 9.46 trillion kilometres).

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This list includes superclusters, galaxy filaments and large quasar groups (LQGs). The structures are listed based on their longest dimension.

This list refers only to coupling of matter with defined limits, and not the coupling of matter in general (such as, for example, the cosmic microwave background, which fills the entire universe). All structures in this list are defined as to whether their presiding limits have been identified.

There are some reasons to be cautious about this list:

• The Zone of Avoidance, or the part of the sky occupied by the Milky Way, blocks out light from several structures, making their limits imprecisely identified.
• Some structures are too distant to be seen even with the most powerful telescopes.
• Some structures have no defined limits, or endpoints. All structures are believed to be part of the cosmic web, which is a conclusive idea.^{[clarification needed]} Most structures are overlapped by nearby galaxies, creating a problem of how to carefully define the structure's limit.
• Interpreting the observational data requires assumptions about gravitational lensing, redshift, etc.

Voids are immense spaces between galaxy filaments and other large-scale structures. Technically they are not structures. They are vast spaces which contain very few or no galaxies. They are theorized to be caused by quantum fluctuations during the early formation of the universe.

A list of the largest voids so far discovered is below. Each is ranked according to its longest dimension.