The arrangement of the radicals follows the contemporary conceptions of the universe, which is based on "one" 一, "above" 上, "religious matters" 示, the trinity Heaven, Earth and Man 三, and king 王, and ends with objects of human craftsmanship, like carts and tools, and the element earth 土, one of the five processes (wuxing 五行). The last radicals are the higher numbers and celestial stems and terrestrial branches. The sequence of the radicals was explained by later commentators of the Shuowen. It many cases the sequence is graphically, with the next character being derived from a part of the preceeding one, for instance:
• 小 "small"
• 八 "to separate"
• 釆 "to distinguish"
• 半 "things divided in the middle"
• 牛 "cattle"
• 牦 "Tibetan yak"
• 告 "marking a dangerous bull"
• 口 "mouth"
• 凵 "a mouth is opened widely"
• 吅 "to shout in alarm"
• 哭 "to weep"
• 走 "to walk"
• 止 "base"
• 癶 "blocked feet"
• 步 "to go"
• 此 "to stop"...
or
• 日 "sun"
• 旦 "dawn"
• "morning sun"
• "weaving streamers"
• 冥 "dark"
• 晶 "brilliant"
• 月 "moon"
• 有 "what should better not occur"
• 朙 "bright"
• 囧 "interlocking windows illuminate the room"
• 夕 "evening"
• 多 "endless repetition"
• 毌 "to penetrate and lock together"
• ㄢ "to include firmly"...

The characters listed under each radical are arranged in a very complicated sequence not easily to perceive. Words with positive connotations are listed first, those with negative meanings last. Technical terms important for state rituals and in the world of thought are also listed relatively before very common words. Words with similar meaning are listed in one group. Within such groups, tautologies are very common (X is Y.//Y is X.). Without index it is therefore very time-consuming to detect a character. At the end of each radical paragraph, the total number of characters listed under the particular radical is stated, as well as the additional writing variants with old and large seal script characters. Later scholars have added some characters not listed in the Shuowen. These are listed as newly appendend (xinfu 新附) at the end of each radical section.
For each character, the meaning is provided first. Then Xu Shen analyses the character itself. In many cases he quotes from the Confucian classics to provide the reader with an example from the literature he knows. Sometimes he also adds a phonetic instruction of the type of du ruo X 读若某 "read like X". In the last place he gives alternative writings (often another radical) or the ancient shape of the character, which often totally differs from the small seal script style.

The Shuowen jiezi lists 9,353 characters as a lemma, and 1,163 alternative characters (old styles, and so on). This large number covers practically all words occurring in the ancient literature. Some characters have later been added, especially such from Han period literature not used in pre-Han texts. The Shuowen does not cover characters from the ancient state of Chu 楚, memory of which was lost during the Han period, and not those exclusively used on bronze vessel inscriptions from the early Zhou period 周 (11th cent.-221 BCE). It does of course also not list the most ancient form of Chinese characters as used in the oracle bone inscriptions from the Shang period 商 (17th-11th cent. BCE) that were only discovered in the early 20th century. It was, nevertheless, easier to read these inscriptions with the help of the Shuowen jiezi. Without Xu Shen's indications, this would have been far more difficult.

Xu Shen's analysis is enormeously helpful for understanding the history of Chinese characters and the original meaning of them. Without his providing the seal script shape and its analysis, it would not be possible to really perceive the acutal meaning of a lot of characters, because the modern chancery script shape is often simplified and does not reveal the origional shape, like 夜 "night", derived from 夕 "evening", 亦, derived from a standing person 大, or 春 "spring", which is a composition of 艹 "grass", 日 "sun" and 屯 "sprout". The Shuowen jiezi served as a model for all later character dictionaries based on an arrangement of the characters according to radicals.
Unfortunatley the Shuowen jiezi has suffered from an unhappy history of transmission. The Tang period scholar 唐 (618-907) Li Yangbing 李阳冰 edited the Shuowen after he had made a lot of amendings concerning the small seal script of the lemmas. He also added his own commentary, which was, according to testimony of later scholars, very unreliable and unscholarly. It was only during the Five Dynasties period 五代 (907-960) that the brothers Xu Xuan 徐铉 and Xu Kai 徐锴 from the state of Southern Tang 南唐 (937-975) started recovering the ancient text of the Shuowen jiezi. Xu Kai published it with his own commentary in the 40 juan "scrolls" long Shuowen jiezi jichuan 说文解字系传.

Xu Xuan became a subject of the Song dynasty 宋 (960-1279) and presented his own, much shorter, commentary to the Shuowen jiezi, to the Song court. He had eliminated the errors by Li Yangbing and added a pronunciation guide according to the fanqie system 反切 used in Sun Mian's 孙愐 character dictionary Tangyun 唐韵 from the Tang period, and some notes to a part of the characters. He divided each of the 15 original chapters into two half-chapters. It was also he who added the new characters to the text which appear in ancient writings, especially such from the Han period, but which were missing in the original Shuowen jiezi. Xu Xuan's imperially acknowledged version (also called Da-Xu ben 大徐本 "Version of the older Xu") was printed, as well as the version of his brother (the Xiao-Xu ben 小徐本 "Version of the younger Xu"). The first is included in the collectaneum Sibu congkan 四部丛刊. The original print from the Song period was owned by the Jiguge Studio 汲古阁, later by Lu Xinyuan 陆心源, and now by the Seikadō Library 静嘉堂文库 in Tokyo. It has also been included in Sun Xingyan's 孙星衍 collectaneum Pingjinguan congshu 平津馆丛书. This version has been reprinted several times and is very widespread. A manuscript version from the Shugutang Studio 述古堂 of Xu Kai's Shuowen jiezi xichuan has been reprinted in the collectaneum Sibu congkan. It has also been printed by the Qing period publisher Qi Guizao 祁嶲藻.
There is a Tang period manuscript preserved, but only in a very small fragment of 188 characters from the section of the radical 木 "tree". It has been commented and published by the Qing period 清 (1644-1911) scholar Mo Youzhi 莫友芝 with the title of Tang xieben Shuowen jiezi mubu jianyi 唐写本说文解字木部笺异. The original is now kept in the Kyō'u shōku Library 杏雨书屋 in Osaka. Another fragment from the section of the radical 口 "mouth" is a manuscript written in Japan.

Xu Kai has also written an index to the Shuowen jiezi, the Shuowen jiezi yunpu 说文解字韵谱, in which the characters are arranged according to the rhyme system valid since the Tang period. The index has later been amended by Xu Xuan. The Southern Song period 南宋 (1127-1279) scholar Li Tao 李焘 has written another index, Shuowen jiezi wuyi yunpu 说文解字五音韵谱, which is geared to the Song period rhyme system, which has less rhyme groups than that of the Tang period. All three books have been printed.
The corpus of Qing period studies on the Shuowen jiezi is quite vast. It has attracted the attention of scholars of all fields, from paleographers and phonologists to botanists. The most important studes and commentaries are Duan Yucai's 段玉裁 Shuowen jiezi zhu 说文解字注, Gui Fu's 桂馥 Shuowen jiezi yizheng 说文解字义证, Wang Yun's 王筠 Shuowen judu 说文句读, and Zhu Junsheng's 朱骏声 Shuowen tongxun dingsheng 说文通训定声.
The book of Duan Yucai is a very detailed analysis of the whole text of the Shuowen jiezi. He quotes a lot of ancient literature in his analysis of the meaning Xu Shen has attributed to the character, in order to trace the expansion of the original meaning of the character. This was often done by borrowing the character for another word. Duan also tries to establish the original pronunciation of the character. Inspite of some errors, the Shuowen jiezi zhu is an excellent early modern standard commentary.
The book by Gui Fu is in first case a source book providing a lot of material from original sources supporting or contradicting the analysis of Xu Shen. Of secondary importance is Gui's analysis of the main text and of the commentaries of the Xu brothers.

The book of Wang Yun has been compiled as an extract of the large works of Duan and Gui, to make it easier for the reader to deal with the large amount of material. Wang has also made some corrections to the text. He has also written the Shuowen shili 说文释例, an analysis of the basic guidelines with which the Shuowen had been written.
Zhu Junsheng has arranged the characters according to rhyme groups. He analyses the original text of Xu Shen and the particular parts of the characters, the exended meaning (while Xu Shen only provides the original meaning of the character) and for which words the character is borrowed. Zhu also adds some more characters from Han and Wei period 曹魏 (220-265) sources not included in the Shuowen jiezi text.

In 1928 Ding Fubao 丁福保 published a compilation of all previous commentaries to the Shuowen in a large, eight volume (modern reprints have even more volumes) edition called Shuowen jiezi gulin 说文解字诂林. The commentaries are assembled according to the characters, so that it is very easy to see all comments under one single heading.

Table of the 540 Shuowen radicals (pdf).