There are several methods of transliteration from Devanāgarī to the Roman script (a process known as romanization) which share similarities, although no single system of transliteration has emerged as the standard.
The International Alphabet of Sanskrit Transliteration (IAST) is a subset of the ISO 15919 standard, used for the transliteration of Sanskrit, Prakrit and Pāḷi into Roman script with diacritics. IAST is a widely used standard. It uses diacritics to differentiate between retroflex and dental consonants (e.g. making dental द=d and retroflex ड=ḍ, which is more readable but requires diacritic printing).
The Hunterian system is the "national system of romanization in India" and the one officially adopted by the Government of India.
The Hunterian system was developed in the nineteenth century by William Wilson Hunter, then Surveyor General of India. When it was proposed, it immediately met with opposition from supporters of the earlier practiced non-systematic and often distorting "Sir Roger Dowler method" (an early corruption of Siraj ud-Daulah) of phonetic transcription, which climaxed in a dramatic showdown in an India Council meeting on 28 May 1872 where the new Hunterian method carried the day. The Hunterian method was inherently simpler and extensible to several Indic scripts because it systematized grapheme transliteration, and it came to prevail and gain government and academic acceptance. Opponents of the grapheme transliteration model continued to mount unsuccessful attempts at reversing government policy until the turn of the century, with one critic calling appealing to "the Indian Government to give up the whole attempt at scientific (i.e. Hunterian) transliteration, and decide once and for all in favour of a return to the old phonetic spelling."