Guru Nanak invented the Gurumukhi characters by simplifying the Sanskrit characters. The holy Granth of the Sikhs is in Gurumukhi. It is worshipped by the Sikhs and the Sindhis. Every Gurudwara has a Granth Sahib. The holy Granth, popularly known as Adi Granth, contains the hymns of the first five Gurus. They were all collected, arranged and formed into one volume called Guru Granth Sahib by the fifth Guru.

It contains a few selections from the hymns of Kabir and other contemporary Vaishnavite saints. Later on, the hymns of the ninth Guru were incorporated in the holy Granth by the tenth Guru. The compositions of Guru Nanak are very extensive.

The Granth Sahib starts with the following :

"There is but one God whose name is true—the Creator". It contains a code of high morals. Purity of life, obedience to Guru, mercy, charity, temperance, justice, straightforwardness, truthfulness, sacrifice, service, love and abstinence from animal food are among the virtues on which great emphasis is laid; while lust, anger, pride, hatred, egoism, greed, selfishness, cruelty, backbiting and falsehood are vehemently condemned.