Fritzl, 73, who has confessed to holding his daughter Elisabeth, 42, captive in a concrete bunker underneath the family home, has been charged with murder, rape, incest, enslavement and false imprisonment and faces a maximum sentence of up to 20 years. Fritzl has denied murder and slavery, but admitted all the other charges.
The trial, one of the most sensational cases in Austria's history, before the eight-member jury is scheduled to last five days and a verdict is expected by Friday. Most of the court's sessions will be held behind closed doors.
Fritzl locked Elisabeth in a soundproof basement at the family home shortly after she turned 18. Over the next 24 years, Fritzl used her as his sex slave, forcing her to have sex with him over 3,000 times.
Elisabeth was forced to give birth to seven children on her own without medical assistance - Fritzl was only present at the birth of one child - three of the children were adopted by Fritzl, while three remained in the basement.
Fritzl is accused of murdering the seventh child, a boy, who died shortly after birth in the basement, and received no medical treatment. He burned the body in an incinerator shortly after its birth. An eighth child miscarried.
However, an Austrian lawyer Dr Raoul Wagner said the charges against him have "little chance of working to keep Fritzl in jail for life" as the court has only "Elisabeth's word, and the body was allegedly burnt and the ashes scattered in the garden."
Although Fritzl was sane and fit for the trial, he was diagnosed with a "serious personality disorder" and could be admitted to a mental institution where he would receive psychiatric care instead of going to jail.
Wagner said that in accordance with Austrian law, Fritzl could be released within six and a half years if he is found not guilty of murder and slavery.
"In a case like this the Austrian legal system is a nonsense. In America, for 3,000 rapes [the number he allegedly committed] a person would face 30,000 years in jail," the lawyer said.
The shocking case came to light in April last year when one of the children Fritzl fathered with Elisabeth was taken to a hospital with a serious medical condition. Kerstin, 19, has since recovered and is living with her mother and five siblings at an undisclosed location.
Fritzl's wife, Rosemarie, said she knew nothing about what went on in the basement. She believed her daughter had joined a religious cult, and had left the three children on the doorstep because she could not take care of them.
The Fritzls' home in Amstetten was bulldozed by the authorities back in November.