HIV can be transmitted from an infected person to another through:

Blood (including menstrual blood)
Semen
Vaginal secretions
Breast milk
Blood contains the highest concentration of the virus, followed by semen, followed by vaginal fluids, followed by breast milk.

* Activities That Allow HIV Transmission

Unprotected sexual contact
Direct blood contact, including injection drug needles, blood transfusions, accidents in health care settings or certain blood products
Mother to baby (before or during birth, or through breast milk)
Sexual intercourse (vaginal and anal): In the genitals and the rectum, HIV may infect the mucous membranes directly or enter through cuts and sores caused during intercourse (many of which would be unnoticed). Vaginal and anal intercourse is a high-risk practice.

Oral sex (mouth-penis, mouth-vagina): The mouth is an inhospitable environment for HIV (in semen, vaginal fluid or blood), meaning the risk of HIV transmission through the throat, gums, and oral membranes is lower than through vaginal or anal membranes. There are however, documented cases where HIV was transmitted orally, so we can’t say that getting HIV-infected semen, vaginal fluid or blood in the mouth is without risk. However, oral sex is considered a low risk practice.

Sharing injection needles: An injection needle can pass blood directly from one person’s bloodstream to another. It is a very efficient way to transmit a blood-borne virus. Sharing needles is considered a high-risk practice.

Mother to Child: It is possible for an HIV-infected mother to pass the virus directly before or during birth, or through breast milk. Breast milk contains HIV, and while small amounts of breast milk do not pose significant threat of infection to adults, it is a viable means of transmission to infants.

The following “bodily fluids” are NOT infectious:

Saliva
Tears
Sweat
Feces
Urine
See also:

How can I tell if I’m infected with HIV?