The large notebooks' contents were the product of the band's work and were "some of the stupid things we wrote down" before reaching final versions of hits including "Hotel California," said Henley, currently on a farewell world tour.
"They (were) not supposed to be seen," said Henley, 76, who wore a suit and tie.
Opposite him, three collectors were in the dock: Craig Inciardi and Edward Kosinski who are charged with criminal possession of stolen goods, and Glenn Horowitz who is charged with attempted criminal possession.
All have pleaded not guilty, claiming to have legally acquired the disputed papers.
The case dates back to the late 1970s, when an author hired by the California rock band to write its biography was entrusted with the notes, which he never returned.
Henley characterized this as theft, although the defense argues that the author is not on trial.
According to the Manhattan district attorney, the author eventually sold the pages in 2005 to Horowitz, a rare book dealer, who in turn sold them to Inciardi and Kosinski.
Years after the band's split, the musician saw a few pages surface on the internet, for the first time in 2012.
Henley ended up acquiring them himself, for $8,500, because it was "the most expedient... most practical" way to reacquire the lyrics.
"I was buying my property back," he said.
Other pages surfaced at auctions over the following years, including a batch of thirteen pages, handwritten for the song "Hotel California".
"I was already extorted once," said Henley, who in 2016 complained to the Manhattan prosecutor's office, which brought the charges.
The trial will last several days.
