Sufism, often described as "the spiritual dimension of Islam", is a way of life centred on cultivating noble character and attaining states that draw the servant closer to his/her Lord. As the foundation of Islam, tawhid (Oneness of God) occupies a central position in Sufi thought and practice. Sufis have engaged in extensive discourse on tawhid, guided by the Qur'an and the Sunna of the Prophet Muhammad (PBUH). However, certain Sufis have faced criticism, with their understanding of tawhid questioned and even accusations of disbelief levelled against them. This has often arisen from misunderstandings surrounding the Sufi concept of "fana'" (spiritual annihilation), the misinterpretation of their metaphorical language, and the decontextualisation of their statements from their broader teachings and lives. This book begins with chapters exploring the meaning and history of Sufism and the concept of tawhid in Islam and Sufism. It then presents a selection of sayings from prominent Sufis, from the first generation of Muslims to the present day, illuminating various aspects of tawhid within the Sufi tradition. These sayings demonstrate that Sufis perceive human cognition as inherently limited in comprehending the Divine Being and stress that true glorification of Allah requires acknowledging this limitation and accepting divine self-disclosure without excessive rationalisation.