Madhab is a certain view related to religious law which is believed to be the truth because it is obtained using the ijma or qiyas method. The school of thought has become a system and has even become a lifestyle inherent in the Nahdliyin of the Nahdatul Ulama community. This paper is a qualitative-descriptive research with a historical approach. The data collection technique uses a literature review that is relevant to the research topic. Data analysis using thematic approach (thematic approach). The results showed that the Nahdliyin Nahdlatul Ulama had applied 4 schools of thought (Shafii, Hanafi, Maliki, Hambali) in their lives, because the Ulama founders of these schools believed that the 4 schools had historical closeness to the Prophet Muhammad Saw. This means that the 4 schools of thought are in accordance with the Qur'an and Hadith. Abstrak Mazhab merupakan pandangan tertentu terkait dengan hukum agama yang diyakini sebagai kebenaran karena diperoleh dengan menggunakan metode ijma atau qiyas. Mazhab telah menjadi sebuah sistem bahkan menjadi gaya hidup yang melekat dalam diri Nahdliyin komunitas Nahdlatul Ulama.  Tulisan ini merupakan penelitian kualitatif-deskriptif dengan pendekatan historis. Teknik pengambilan data dengan menggunakan kajian pustaka (literature review) yang relevan dengan topik penelitian. Analisis data dengan menggunakan pendekatan tematik (thematic approach). Hasil penelitian menunjukkan bahwa para Nahdliyin Nahdlatul Ulama telah  menerapkan 4 mazhab (Syafi’i, Hanafi, Maliki, Hambali) di dalam kehidupannya, karena para tokoh Ulama pendiri mazhab tersebut memiliki keyakinan bahwa ke-4 mazhab tersebut memiliki kedekatan historis dengan Nabi Muhammad Saw. Ini berarti ke-4 mazhab sesuai dengan Al-Qur’an dan Hadits.

Ahlussunnah wal-Jama`ah (Aswaja) an-nahdliyah Islam is the frame of the Unitary State of the Republic of Indonesia (NKRI). The founders of NU and the founders of this country are identical people. In their view, Indonesia is now no longer at war with Islam, they firmly stated that establishing the Unitary State of the Republic of Indonesia is one of their responsibilities in maintaining and implementing non-secular shari'ah. The Muslim community, especially NU, has a strategic function in building a spirit of war against colonialism as well as being a unifying element of the nation and state, so that it is only natural that the most effective until now is that we are at the forefront of being protective and caring for the Unitary State of the Republic of Indonesia. Caring for the Unitary State of the Republic of Indonesia through values Aswaja's values ​​demand the use of information media. More or less, NU already knows it. Apart from publishing print media such as Ar-Risalah, Hall, and the like, NU has also taken advantage of the internet by spreading NU Online since 2003. From this, the slogan "Technology as Tradition" was born. Hopefully the integrity of the Unitary State of the Republic of Indonesia can be maintained until the appointed time, through the integration of Aswaja An-Nahdliyah values ​​into the lifestyle of the state and Islamic faith on this earth. The true teachings of Ahlusunah wal Jama'ah Islam which can be upheld through means Nahdlatul Ulama is very closely related to the State of Indonesia. These teachings are at-tawassuth (central mindset), at-tawazun (balanced), al-i'tidal (perpendicular), and tasamuh (tolerance). The relationship between the Aswaja Annahdliyah studies within the Indonesian State is in accordance with the noble ideals of the Indonesian nation. His mindset that upholds tolerance and moderation has made him widespread within Indonesia. We will continue to impart many noble values ​​from Nahdlatul Ulama, namely the homeland of Indonesia. As an original Indonesian organization, NU also has a good influence in the Indonesian state. Indonesia is considered pleasant because NU's mindset is balanced, tolerant and light. Aswaja values ​​are very vital to be developed in Islamic development in Indonesia today. In addition, the Aswaja training emerged because of the desire of the Indonesian people, especially as understanding in non-secular training and moral formation, male or female, and noble male or female. The inculcation of Aswaja values ​​cannot be most effectively carried out in formal academic institutions, but is also aimed at a wider network (non-formal and casual training). For example, regular recitation programs packed with ulema' are very good for cultivating non-secular value expertise in society. It also aims to strengthen men or women, morality, and men or women from the network. Men or women from well-formed networks turn into extraordinary men or women from nations and countries as well.    

The 33rd NU Muktamar in Jombang 2015 mandated about 'developing other businesses through collaboration with domestic and foreign parties that benefit the community at large in order to realize the khaira ummah' (AD/ART NU, Article 9). Since the 13th NU Muktamar in Pandeglang 1939, NU has initiated Mabadi' Khaira Ummah (MKU). MKU is the basic principle of forming an ideal society. MKU consists of five basic principles, namely, ash-shidqu (true not lying, trust) al amanah wal-wafa bil 'ahdi (trust, keeping promises, loyal, commitment), at-ta'awun (helping, mutual helping), al adalah (fairness) and al istiqamah (firmness, constancy, consistency). In the midst of the era of industry 4.0 and society 5.0 as it is today, MKU is of course very urgent to provide a harmonious balance so that the goals of industry 4.0 productivity with the human life convenience of society 5.0 in various parts of the world can take place sustainably and full of grace. MKU is also becoming increasingly important alongside the 18 values ​​of character education.