The Courtship of Princess Leia is only one book, and a controversial one at that. Some loved it, others hated it. But it has to be given credit for two of the most popular cultures in the EU. It is set 4 years after the destruction of the 2nd Death Star.
It introduces the world of Dathomir, home of the witches of Dathomir. These Force Users are descended from a rogue Jedi. Those among them who use the Force or magic for the Dark Side are called Nightsisters. The world is largely a primitive wilderness, and the witches often use rancors as transportation. In the time of the Empire, it was an interdicted planet.
It also introduces the Hapan Empire, another world ruled by woman. Unlike Dathomir, this is an entire group of planets. Led by a ruthless Queen mother, the people there are human and by most standards beautiful. They are descendants of pirates, the Lorell Raiders. The male pirates kidnapped beautiful woman and took them home. However eventually the pirates were destroyed by the Jedi and the woman and children were left to fend for themselves. They shunned the outside galaxy during both the Old Republic and the Empire.
Chief Characters:
Princess Leia Organa
Han Solo
Luke Skywalker
Chewbacca
R2-D2
C3PO
Augwynne Djo (Head of the Singing Mountain Clan)
Tenenial Djo (Member of the Singing Mountain Clan)
Ta’a Chume (Queen Mother of the Hapes Cluster)
Prince Isolder (Heir to the Hapes Cluster)
Gethzerion (Nightsister)
Warlord Zsinj (Imperial warlord)
Han Solo has been chasing Imperial warlord Zsinj for months. Now he’s finally coming home to his beloved Princess. But on arrival, he finds that Princess Leia’s mission to open diplomatic ties and borrow money from Hapes has had unexpected results. The Hapans have agreed…on the condition Leia marry Prince Isolder, heir to the throne.
To his horror, Leia, torn between how the Hapan worlds reminded her of Alderaan and her duty to the needs of the Republic, seems interested. When Leia refuses to give him equal time, he goes off and in desperation wins a serious sabaac game…the most serious in years. He wins the planet Dathomir.
But the planet is in the presumed dead warlord’s territory. Heartbroken and desperate, he kidnaps Leia and spirits her off to Dathomir. But Leia is furious at his apparent betrayal, Zsinj is not only not dead, but has a prison on the planet, and they get shot down, encountering both the suspicious Singing Mountain Clan (who still keep men as slaves) and the nightsisters who at all costs must not be allowed to leave the planet.
Luke Skywalker has been pursuing leads on long lost Jedi teachings. One leads him to a brief message involving Yoda, a ship called the Chu’unthor and Dathomir. He abandons this pursuit on hearing of the crisis.
Luke and Prince Isolder team up and race against the Queen Mother, the Nightsisters, and Zsinj to find Han and Leia first.
SPOILER WARNING for the End of Courtship of Princess Leia.

Prince Isolder marries a woman of Dathomir, their daughter, Tenel Ka, joins the Jedi Academy and is a friend in many adventures with Jacen and Jaina Solo. In the future, these political ties prove to be a great help to the Jedi.
Star Wars Jedi Search (which was released the same year) introduces Kirana Ti, a witch of Dathomir who joins the Jedi Academy.
The nightsisters, decades later are recreated and join with forces with the Shadow Academy.
Allana, daughter of Tenel Ka, has an unknowing influence on the decisions of Jacen Solo in both the Swarm Wars and the Legacy of the Force series.
In Fate of the Jedi, it is revealed that a Jedi Enclave had been formed on Dathomir since the end of the Yuuzhan Vong War. A sith apprentice fleeing Luke and Ben Skywalker hides there amongst the witches, and they find themselves battling nightsisters to survive as well as help the clans.

Darth Maul (Dark Horse) reveals a nightsister working with the Black Sun Crime Syndicate

Star Wars Republic, Infinities End (Dark Horse Comics) introduces the nightsisters attempt to reactivate the Infinity Gate, an ancient device that can destroy worlds (as a side effect!). The first face painted or tattooed versions of the witches appeared here.
The Chu’unthor is also mentioned.
In Darth Maul, Son of Dathomir by Dark Horse Comics, Darth Sidious clashes with the witches and has a one on one battle with the leader of the nightsisters.
In the novel The Last Jedi, Jax Pavan travels to Dathomir to enlist the witches aid and meets with the Singing Mountain Clan and a (younger) Augwynne Djo. This book actually is the first to add The Clone Wars TV interpretation of the Witches of Dathomir, the Infinity Gates story line and the Courtship version of the witches all in one sitting.