With no axial tilt and a perfectly circular orbit, Kashyyyk experienced one continuous season. It was composed of a molten metallic core, rocky mantle, and a silicate rock crust. The planet had four continents, making up 40% of the surface, which were mostly covered in lush, wroshyr tree-filled forests, which were several kilometers high. The planet did have a small amount of desert region in the rain-shadow of its small mountain ranges as well as large plains including the Woolwarricca region. A tropical ocean belt contained archipelagos and long coral reefs. In addition, a few sandy beaches could be found along the shores of its oceans. The Kashyyyk coastlines were lined with a brownish-white sand and thick grasses. Kashyyyk's highest peak was Korrokrrayyo Mountain.
Much of the planet could be compared to a giant swamp—filled with wildlife and covered with wet soil and large amounts of water. The prevalent ecology could be politely described as a "layered deathtrap", as the dangers presented by local wildlife increased as one descended toward the forest floor. According to Wookiee culture, this vertical environment consisted of seven levels. The bulk of Wookiee civilization was located on the uppermost seventh level, and even the bravest Wookiees rarely ventured below the fourth level. Unlike most, Chewbacca was known to travel below this marking point for most Wookiees. The ground level was known as the Shadowlands and, sometimes, the "notherworld".
As previously stated, the wroshyr trees were the dominant flora. Wroshyr trees may have actually been one large connected organism, as when limbs of two tree limbs ran into each other, they would fuse together. The Wookiees inferred great symbolism in this. Jolee Bindo theorized that the species of wroshyr tree is in fact alien to the planet and was planted there by the Infinite Empire. This was based on information given by a Rakata computer left near one of their ancient Star Maps.
The forests of Kashyyyk were filled with a tremendous variety of plant life, many with some form of consciousness. The Wookiees learned to communicate with these plants and often came to an understanding about their use. One example of this was with the Orga plants, who allowed the Wookiees to harvest their older roots to use in Life Day ceremonies.
Most other flora was parasitic to the wroshyr trees, grew in dirt pockets in crevices of the trees, or were carnivorous.
There were at least two types of large carnivorous plants in the lower levels. These included a carnivorous, spiked vine plants, and the infamous Syren plant, which played a crucial role in the coming of age rituals for various Wookiee tribes. Both of these plants were capable of consuming adolescent Wookiees or fully grown Humans.
Besides the primary sentient Wookiees, Kashyyyk was home to various species of banthas, a small population of terentateks, and a host of other species. Usually, the deeper into the jungle one went, the more dangerous the animals became. For instance, the tenacious and intelligent Kashyyykian giant weaver—a giant red-pigmented spiderlike creature—could track prey for over a kilometer and coordinate with other weavers to organize an ambush. Additionally, many of the species that inhabited the deeper parts of the jungle were capable of bio-phosphorescence, since the deeper layers of the forest were in perpetual darkness.
However, victory was short-lived for the Wookiees. With the rise of the Galactic Empire, the Jedi were branded enemies of the Republic/Empire as Supreme Chancellor Palpatine made himself Emperor and initiated Order 66. The clone troopers then took control of Kashyyyk, killing Luminara Unduli, sending Quinlan Vos into hiding, and forcing Yoda to kill Gree and discreetly escape from the battle on a Can-cell. Later Yoda escaped the planet, with the help of Tarfful and Chewbacca via a former Republic Escape pod. The Empire was quick to suppress Kashyyyk by renaming it "Wookiee Planet C" (as it was the third orbit in its system) and placed it under martial law. Several months later, a group of Jedi including Olee Starstone went to Kashyyyk to search for the other Jedi who had been there. The Empire, led by Darth Vader, tracked them and attacked the planet. In response, the Wookiees rebelled against their oppressors, but were ultimately unsuccessful. Clone troopers attempted to land, but many were shot down by abandoned Confederate weaponry utilized by the Wookiees. Darth Vader landed and killed two Jedi before being stopped by Master Roan Shryne, who also died at Vader's hand. The orbital fleet bombarded the planet, causing severe damage on the surface. Wookiees either escaped into the undergrowth or into space, where they were stopped by a Detainer CC-2200 interdictor cruiser. Starstone had slicer Filli Bitters slice into an abandoned CIS ship and crash it into the interdictor cruiser. Many refugees escaped, including Starstone and her Jedi friends, Filli and his smuggling group, and Chewbacca. The Empire occupied the planet, allowing then-Moff Wilhuff Tarkin, one of the Imperial commanders that participated in the battle, to capture and export Wookiees as slave labor to Despayre, in order to help construct the First Death Star.
In 18 BBY, Mallie Marek was killed by the remnant of the droids and Trandoshans from the battle a year prior. Almost immediately, her death caused Palpatine to sense Kento’s presence on Kashyyyk, thus he sent Vader to eliminate him. Vader and his troops met heavy resistance from the local Wookiee population, but ultimately the 501st Legion succeeded in crushing the uprising. During the battle, Vader bested and killed Kento Marek. Upon discovering his opponent's son Galen Marek, whom he found to be extremely powerful in the Force, Vader exterminated all witnesses, including the stormtrooper commander, and went on to train the boy as his secret apprentice.
During the occupation, Kashyyyk was open by the Imperial authorities to slavers from neighboring Trandosha and Mytaranor. At the advice of the Trandoshans, the Empire began using the powerful Wookiees to carry out slave labor. Wookiee captives were used for countless Imperial projects, including the Maw Installation. However, because of their devotion to their homeworld, many Wookiees would evade the Imperial garrison there to revisit their beloved forests for important Wookiee holidays such as Life Day.
In 2 BBY, Princess Leia Organa of Alderaan was secretly sent by Emperor Palpatine to be held as a hostage on the planet, in order to keep her adoptive father from speaking out against the Empire. Leia was placed under custody of the local commander, Captain Ozzik Sturn, who used to hunt Wookiees for sport, and confined in her private quarters. Eventually, she was rescued by Galen Marek, himself on a mission by Jedi Master Rahm Kota to track down Bail Organa. Leia promised to reveal the location of her father, but only if Galen was able to destroy a skyhook, which was designed to transfer Wookiees offworld for slave labor. Galen headed to the construction site, slaying Captain Sturn and destroying the skyhook. According to Galen however, "the Empire would just rebuild it". Grateful for Galen's heroic deeds, Leia informed him that Bail had journeyed to Felucia, causing a chain of events that culminated in the signing of the Corellian Treaty.
Later, after Marek's death at the hands of Emperor Palpatine, Leia Organa met with Bail Organa, Mon Mothma, Garm Bel Iblis, Rahm Kota, Juno Eclipse and PROXY. In which they formed the Rebel Alliance. Leia picked a symbol for the Alliance, the symbol of the Marek family, in a tribute to Galen Marek, his family and his victories against the Empire.
One year after the destruction of the first Death Star, Kashyyyk has been subjected to a long orbital blockade. Darth Vader ordered a door-to-door curfew in order to apprehend every Rebel, eventually hoping to get his hands on the crew of the Millennium Falcon. However, the Imperials were defeated by Lumpawaroo on Rwookrrorro, and subsequently, the Wookiees, along with the local Alliance members, celebrated Life Day.
Moff Darcc, the Imperial governor of Kashyyyk who ruled planet from his private palace, forged a pact with the Trandoshan slaver Pekt, appointing him to oversee the entire slaving operation. They have finally installed Avatar Orbital Platform in orbit of the planet, to help further enslavement of the Wookiees.