Forgotten Realms:

Lizardfolk were semi-aquatic reptilian humanoids. Their skin was covered in scales and varied in color from dark green through to shades of brown and gray. Taller than humans and powerfully built, lizardfolk were often between 6 and 7 feet (1.8–2.1 m) tall and weighed between 200 and 250 pounds (90.7–113 kg). Lizardfolk had non-prehensile muscular tails that grew to three or four feet in length, and these were used for balance. They also had sharp claws and teeth. Although non-reptilians struggled to tell the difference between males and females, lizardfolk could easily distinguish themselves. Lizardfolk had no interest in money or jewels. They also did not much value accumulating knowledge if it was not practically useful. They largely valued things based on whether or not it was good to eat. If it was, it quickly got their attention; if not, it was ignored. Lizardfolk could often become distracted at the appearance of food, even if they were in combat. They were easier to parley with after a meal, and a hungry lizardfolk was completely obstreperous. Lizardfolk could be highly dangerous when provoked. However, they were not inherently evil; they were simply savage and had a hard time fitting in with the civilized world. Those that ventured into towns or cities were often alarmed, frightened, or offended by the environment. Few tried to adapt, let alone assimilate into Faerûnian societies. Instead, they felt their part was to learn about "softskin" ways and in turn show them how "real people" lived. Lizardfolk had to keep their skin relatively moist and needed to wet their bodies regularly if they were in dry climates. For this reason they were particularly fearful of desert landscapes.  

Greyhawk:

Lizardfolk are primitive reptilian humanoids that can be very dangerous if provoked. Although they are omnivores, lizardfolk prefer meat. Lizardfolk make their homes in temperate marshes and swamps. They are passable swimmers however, and may also be found in underwater cave systems. Lizardfolk have been encountered in significant numbers in the Gnatmarsh, the Hool Marshes, the Mistmarsh, the Rushmoors, and the Vast Swamp. Lizardfolk are tall humanoids that look like a cross between a powerfully built human and a lizard. They have a long tail, clawed hands, and a toothy jaw. They are usually six to seven feet in height, with gray, green, or brown scales. Lizardfolk use their tails, typically three to four feet long. Lizardfolk commonly weigh from 200 to 250 pounds. There are several species of lizardfolk however, and these can range from three-foot tall pygmies to nine-foot tall giants. Lizardfolk can hold their breath for a very long time, by human standards.  

Eberron: 

Lizardfolk is a name for the collective reptilian tribes that inhabit the jungles of Eberron. Some lizardfolk, like the poison dusk and blackscale tribes, live in the wilds of Q'barra, where they defend their lands from the human colonists of New Galifar and Hope, destroying what they see as the "human infestation." The coming of humans to Khorvaire has caused nothing but problems for the lizardfolk of Q'barra. 2,400 years ago, the lizardfolk on the coasts of Q'barra faced the plundering of Malleon the Reaver. Then, during the Last War, human colonists came to Q'barra searching for a new life. These humans sought to create settlements on existing lizardfolk lands, and came into conflicts with both the worshipers of the Cold Sun, but also the Cold Sun Federation. Even though the Cold Sun Tribes have negotiated a fragile peace with the new nations of New Galifar and Hope, conflicts between the human settlements and the lizardfolk continue to this day. There are three kinds of lizardfolk in Eberron: Cold Sun, Blackscale, and Poison Dusk. The Cold Sun lizardfolk are more rightfully simply called "lizardfolk", and date back to Eberron's beginning. However, they are frequently called the "Cold Sun" lizardfolk to differentiate them from the other species of lizardfolk: the blackscale and the poison dusk. Most of these species of "original" lizardfolk have banded together to form the Cold Sun Federation, though there are some tribes of lizardfolk that are not part of this federation. The blackscale lizardfolk see themselves as the chosen of Masvirik, the Cold Sun. They cite their black scales as proof that Masvirik's servant Rhashaak favors them over all. The blackscale are Rhashaak's warriors, using their superior strength and their access to the vaults of Haka'torvhak to bully and enslave the other lizardfolk species. They are extremely hostile, and will openly assault any non-reptilian race that they come across. The blackscale often live off the "tributes" made to them by the lesser lizardfolk tribes, especially the poison dusk. However, they will follow the orders of any lizardfolk dragon priest chosen by Rhashaak, no matter what species they may be. Poison dusk lizardfolk are the smallest of the three species of lizardfolk in Q'barra. While they are smaller and weaker, they are also faster and more intelligent. They are highly skilled trackers and hunters, and use everything from poisons to nets to bring down their prey. They prefer to strike from the shadows, and will often use guerrilla tactics, such as poisoning an enemy's food supply, to win the day.