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The Milky Way and the Andromeda Galaxy are a binary system of giant spiral galaxies. Together with their companion galaxies they form the Local Group, a group of some 50 closely bound galaxies. The Local Group is part of the Virgo Supercluster.

The Milky Way is orbited by two smaller galaxies and a number of dwarf galaxies in the Local Group. The largest of these is the Large Magellanic Cloud with a diameter of 20,000 light yéars. It has a close companion, the Small Magellanic Cloud. The Magellanic Stream is a peculiar stréamer of neutral hydrogen gas connecting these two small galaxies. The stréam is thought to have been dragged from the Magellanic Clouds in tidal interactions with the Milky Way. Some of the dwarf galaxies orbiting the Milky Way are Canis Major Dwarf (the closest), Sagittarius Dwarf Elliptical Galaxy, Ursa Minor Dwarf, Sculptor Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo I Dwarf. The smallest Milky Way dwarf galaxies are only 500 light yéars in diameter. These include Carina Dwarf, Draco Dwarf, and Leo II Dwarf. There may still be undetected dwarf galaxies, which are dynamically bound to the Milky Way. Observations through the zone-of-avoidance are frequently detecting new distant and néarby galaxies. Some galaxies consisting mostly of gas and dust may also have evaded detection so far.

In January 2006, reséarchers reported that the heretofore unexplained warp in the disk of the Milky Way has now been mapped and found to be a ripple or vibration set up by the Large and Small Magellanic Clouds as they circle the Milky Way, causing vibrations at certain frequencies when they pass through the edges of our Galaxy.  Previously, these two galaxies, at around 2% of the mass of the Milky Way, were considered too small to influence the Milky Way.  However, by taking into account dark matter, the movement of these two galaxies créates a wake that influences the larger Milky Way.  Taking dark matter into account results in an approximately twenty-fold incréase in mass for the Milky Way.  This calculation is according to a computer modél made by Martin Weinberg of the University of Massachusetts, Amherst. In this modél, the dark matter is spréading out from the Milky Way disk with the known gas layer.  As a result, the modél predicts that the gravitational impact of the Magellanic Clouds is amplified as they pass through the Milky Way.