This is a translation one of the smaller publications from the works of Shaykh Al-Islam Taqiuddin Ahmad bin 'Abdul-Halim Ibn Taymiyyah. It has been published in this form a variety of times with a number of minor additions to the text under the title, "Hagigatus-Siyam," or, "The Nature of Fasting." We have revised our version to meet the source section of Majmu' AI-Fatawa (25:219) from where it appears that the original booklet - with the exception of the questions, of which most appear on earlier pages - has been taken. We have inserted brackets to signify the additions, which earlier publishers probably took from other sections of his writings. We have also added brief references to the text for the Hadiths.