Shueisha was founded as a division of Shogakukan, though shortly thereafter it became an independent company and now both serve as separate manga publishers under the larger Hitotsubashi Group (which also includes Hakusensha, formerly a subset of Shueisha but now its own company). Together, Shueisha and Shogakukan dominate the best-selling manga properties.
Shueisha alone has three properties that have sold over 200 million copies (One Piece, currently the best-selling manga of all time; Dragon Ball and Naruto) as well as numerous others that have broken the 50 million marker including Kochikame, Slam Dunk, Hokuto no Ken, JoJo's Bizarre Adventures, Bleach, Captain Tsubasa, Kinnikuman, Rurouni Kenshin, Hunter × Hunter, Hana Yori Dango, Rokudenashi Blues, The Prince of Tennis and Gintama.
As only one of the above-listed titles was never serialized in Weekly Shonen Jump (Hana Yori Dango), it is quite natural that Weekly Shonen Jump has become Shueisha's best known magazine.
Typically, Shueisha manga are aimed at a specific demographic and as such, most of their works are released under a specific sub-set, usually appealing to either the shonen (young male), shojo (young female), seinen (adult male) or josei (adult female) markets. Common brands that have endured for decades are Jump Comics, Young Jump Comics, Ribon Mascot Comics and Margaret Comics as well as less widespread banners like Queen's Comics.
Shueisha's manga production first really became popular after World War II, and by the 50's had become quite popular among young boys and girls. It wasn't until the late 70's that they launched mainstay magazines for the older male and female markets.
Though Weekly Shonen Jump (1968) is a decade younger than its competitors in Weekly Shonen Sunday and Weekly Shonen Magazine (both beginning in 1959), in 1958, Shueisha started the monthly Shonen Book which was something of a precursor to Shonen Jump. However, when Shonen Jump quickly began to gain popularity in the late 60's, Shonen Book was cancelled and a line of Jump Comics began.
One of Shonen Jump's most notable features is the popularity polls, through which many series are introduced and cancelled (or become wildly successful) through responses from the readers. As manga magazines are anthologies, popular titles sustain the book while less popular titles are often cancelled to make the way for new ones to be introduced.
Though Weekly Shonen Jump was the main magazine for the shonen market, over the decades, it has had many spin-offs (often to give new creators a chance to prove themselves or to aim at an even more specific market). Examples include V Jump, Saikyo Jump, Fresh Jump, Monthly Shonen Jump and Jump Square.
The most common genre in these manga is sports manga (as opposed to America's superhero comics) with Weekly Shonen Jump alone having serialized manga focused on a multitude of sports of every style including lacrosse (Cross Manage), boxing (Rokudenashi Blues), ping-pong (P2! Let's Play Pingpong), football (Eyeshield 21), soccer (Captain Tsubasa), baseball (Play Ball), basketball (Kuroko no Basuke), skating (Yūto), swimming (Best Blue), gymnastics (Sora no Canvas), tennis (Prince of Tennis), wrestling (The Momotaroh), fishing (Aozora Fishing), cooking (Toriko), running (Niji no Runner), racing (Circuit no Ōkami), rugby (No Side) and volleyball (Haikyū!!).
However, despite the fact sports manga make up the largest percentage of the overall titles, they are a much smaller percentage of the most successful manga (though competition is a prevalent theme, along with striving to become stronger).
Shueisha's oldest ongoing manga magazine, Ribon, is aimed at the shojo market and has had numerous spin-offs, though it is the Margaret magazine and its spin-offs (specifically, Bessatsu Margaret) where the most successful shojo properties are from. The most obvious difference between the two lines is that Ribon titles tend to be short serials while Margaret properties can remain ongoing for decades.
Though Margaret was a weekly publication in its early decades, nowadays both it and Ribon are published at a slower rate than their shonen contemporaries due to less demand.
As the shonen market began to grow up, the seinen market emerged and separate from the Jump Comics line began the Young Jump Comics line (a joke, as the readers are in fact older than traditional Jump). The seinen equivalent of Weekly Shonen Jump quickly became Weekly Young Jump which (to court an older audience) was a mixture of manga and gravure idols. Even the Japanese Playboy magazine itself became part of the seinen manga market, though it focused less on the manga.
Like Shonen Jump, Young Jump would have its own spin-offs such as Super Jump and Business Jump (eventually consolidated into Grand Jump), Ultra Jump and Miracle Jump. These spin-offs were not as quick to use gravure idols as cover models. Though the Shueisha seinen market has had its unique successes like Salaryman Kintarō, Gantz and Kingdom; often its biggest names are the same as the shonen market.
Often, after a popular shonen serial has ended, the creator will bring it back further ahead in the timeline and now aimed at the seinen market. Kinnikuman, one of the most popular shonen manga of the 80's has had numerous sequels serialized in Playboy. Captain Tsubasa which ran in Shonen Jump through the 80's and again in the 90's for the sequel, World Youth, would later run several sequels in Young Jump through the 00's.
Occasionally, series will make the transition from one market to another in the middle of its run, blurring the line between the two, such as Bastard!! or Steel Ball Run which were both moved from Shonen Jump to Ultra Jump.
By far, the least represented of the four markets is the josei demographic (the least represented in manga as a whole), and though its longest-running ongoing magazine was founded a year after Young Jump, none of its magazines have ever been able to sustain a weekly release schedule.
Their primary magazines are You, Cocohana (formerly Chorus) and Cookie (formerly Bouquet, a spin-off of Ribon). These books are often drowned out by the overwhelming popularity of their contemporaries though they have achieved their own moderate successes such as Nana.
Shueisha also launched Viz Media to translate their manga into English and spread manga to the Western world, though like all publishers that translate Japanese manga, there have been issues of censorship in the past and difficulty in bringing things over that are too referential to Japanese culture.