Hydrophilicity ( from Ancient Greek ὕδωρ hydor " water " and φίλος philos " loving" ) means they love water, indicating that a substance interacts strongly with water ( or other polar substances). The opposite of hydrophilicity is hydrophobicity.

Hydrophilic agents are often water soluble, it is hydrophilic but also substances which are not soluble in water, such as Hydrogels or colestipol hydrochloride. For this reason, hydrophilic not be equated with water. It only refers to the interaction with water and neither the solubility nor the ability to attract and bind water. A substance that can this is called hygroscopic. Hydrophilic substances are often lipophobic same time, so are poorly soluble in fats or oils. Substances which are hydrophilic and lipophilic, is known as amphiphilic; these include, for example soaps. Amphiphilicity is a specific property of a molecule that bears hydrophobic and hydrophilic groups.

Also, surfaces can be hydrophilic. These are always covered by a mostly invisible film of water. Most metals are hydrophilic, as well as glass surfaces. Hydrophilic surfaces have to water contact angle close to 0 °.

Hydrophilic substances are usually either salts ( ionic compounds ) or polar substances dissolve in polar water also correspondingly good.