The hypothalamic-pituitary-gonadal axis (also HPG axis) is referring to the effects of the hypothalamus, pituitary gland, and gonads as if these individual endocrine glands were a single entity as a whole. Because these glands often behave in cooperation, physiologists and endocrinologists find it convenient and descriptive to speak of them as a single system.

The hypothalamic-pituitary-gonadal axis is a critical part in the development and regulation of a number of the body's systems, such as the reproductive, and immune systems. Fluctuations in the hormones cause changes in the hormones produced by each gland and have various widespread and local effects on the body. This axis controls development, reproduction, and aging in animals. The hypothalamus produces gonadotropin-releasing hormone (GnRH). The anterior portion of the pituitary gland produces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the gonads produce estrogen and testosterone.