In biology, a biological system (or organ system or body system) is a group of organs that work together to perform a certain task. Common systems, such as those present in mammals and other animals, seen in human anatomy, are those such as the circulatory system, the respiratory system, the nervous system, etc.

A group of systems composes an organism, e.g. the human body.

Humans have a variety of systems due to the complexity of the species' organism. These specific systems are widely studied in Human anatomy. "Human" systems are also present in many other animals.

• Circulatory system: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels.
• Digestive system: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, rectum and anus.
• Immune system: The system the fights off Diseases and bacteria.
• Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary or pituitary gland, pineal body or pineal gland, thyroid, parathyroids and adrenals, i.e., adrenal glands.
• Integumentary system: skin, hair, fat, and nails.
• Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the Immune system: defending against disease-causing agents with leukocytes, tonsils, adenoids, thymus and spleen.
• Muscular system: movement with muscles.
• Nervous system: collecting, transferring and processing information with brain, spinal cord, peripheral nerves and nerves.
• Reproductive system: the sex organs, such as ovaries, fallopian tubes, uterus, vagina, mammary glands, testes, vas deferens, seminal vesicles, prostate and penis.
• Respiratory system: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm.
• Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons.
• Urinary system: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine.
• Endocannabinoid system: neuromodulatory lipids and receptors involved in a variety of physiological processes including appetite, pain-sensation, mood, motor learning, synaptic plasticity, and memory.

• Artificial life
• Biological systems engineering
• Systems biology
• Systems ecology
• Systems theory

• Systems Biology: An Overview by Mario Jardon: A review from the Science Creative Quarterly, 2005.
• Synthesis and Analysis of a Biological System, by Hiroyuki Kurata, 1999.
• Semantic Systems Biology