Roundup is a brand name of herbicide originally produced by Monsanto, which Bayer acquired in 2018. Prior to the late-2010s formulations, it used broad-spectrum glyphosate-based herbicides. As of 2009, sales of Roundup herbicides still represented about 10 percent of Monsanto's revenue despite competition from Chinese producers of other glyphosate-based herbicides. The overall Roundup line of products represented about half of Monsanto's yearly revenue in 2009. The product is marketed to consumers by Scotts Miracle-Gro Company. In the late-2010s other non-glyphosate containing herbicides were also sold under the Roundup brand.

Monsanto patented the herbicidal use of glyphosate and derivatives in 1971. Commercial sale and usage in significant quantities started in 1974. It retained exclusive rights to glyphosate in the US until its US patent expired in September 2000; in other countries the patent expired earlier. The Roundup trademark is registered with the US Patent and Trademark Office and still extant. However, glyphosate is no longer under patent, so similar products use it as an active ingredient.

The main active ingredient of Roundup is the isopropylamine salt of glyphosate. Another ingredient of Roundup is the surfactant POEA (polyethoxylated tallow amine).

Monsanto also produced seeds which grow into plants genetically engineered to be tolerant to glyphosate, which are known as Roundup Ready crops. The genes contained in these seeds are patented. Such crops allow farmers to use glyphosate as a post-emergence herbicide against most broadleaf and cereal weeds.

The health impacts of the product as well as its effects on the environment have been at the center of substantial legal and scientific controversies. In June 2020, Bayer agreed to pay $9.6 billion to settle tens of thousands of claims, mostly alleging that glyphosate-based Roundup had caused cancer.

Glyphosate-based formulations may contain a number of adjuvants, the identities of which may be proprietary. Surfactants are used in herbicide formulations as wetting agents, to maximize coverage and aid penetration of the herbicide(s) through plant leaves. As agricultural spray adjuvants, surfactants may be pre-mixed into commercial formulations or they may be purchased separately and mixed on-site.

Polyethoxylated tallow amine (POEA) is a surfactant used in the original Roundup formulation and was commonly used in 2015. Different versions of Roundup have included different percentages of POEA. A 1997 US government report said that Roundup is 15% POEA while Roundup Pro is 14.5%. Since POEA is more toxic to fish and amphibians than glyphosate alone, POEA is not allowed in aquatic formulations.

Non-glyphosate formulations of Roundup are typically used for lawns that glyphosate would otherwise kill. Both type of products being sold under the Roundup brand name can be a source of confusion for consumers. Active ingredients for non-glyphosate formulations of Roundup can include MCPA, quinclorac, dicamba, and sulfentrazone, penoxsulam, and 2,4-D