The beginning and ending of this period are cause for debate, but it is thought the period began with DC Comics Showcase #4 which successfully introduced the modernized version of The Flash. Under the editorship of Julius Schwartz, this was the first of a series of revised old characters into more modern versions such as Green Lantern, The Atom and Hawkman. The success of these character helped the company find a viable genre that could make for successful properties under the restrictions of the Comics Code. This success helped breath in new life in the comic book medium and sales began to recover from the debacle of the blacklash on horror and crime comics.
The period also saw the rise of Marvel Comics under the guidance of writer/editor Stan Lee and artists/cowriters Jack Kirby and Steve Ditko which introduced more complex characters and dynamic plotting to American comics. After an initial period of confusion about the reasons for Marvel's success, DC began adopt some of the same artistic approach.
The end of the period is thought to be in the early 1970s with the departure of Jack Kirby from Marvel, the growing influence of new younger talents like Neal Adams and a generally darker tone in superhero comics typified with an acclaimed run of social commentary heavy stories in the comic Green Lantern/Green Arrow by Dennis O'Neil and Neal Adams.
See also: Golden Age of Comic Books