There are five different opinions about the origin and ancestry of Sindhi language. The first group believes that Sindhi is derived from Sanskrit through Varchada Apabhransha. Dr. Ernest Trumpp was the pioneer of this theory. He (Dr. Trumpp) seemed to be doubtful, 'afterwards', about his theory. In the same book he considers it as an independent languages. He states:
"The Sindhi has remained steady in the first stage of decomposition after the old Prakrit, where all other cognate dialects have sunk some degrees deeper . We shall see in the course of our inductory remarks that the rules which the Prakrit grammarian Kramdishvara has laid down in reference to the Apahransha are still recognizable is present Sindhi, which by no means can be stated of the other dialects. The Sindhi has thus become an independent language, which, through sharing a common origin with its sister tongues is very materially differing from them."
Dr.Trump's theory was first challenged by Dr. N.A. Baloch and then by Mr. Sirajul Haque Memon. Dr. Baloch states:
"Sindhi is ancients Indo-Aryan language, probably having its origin in a pre-Sanskrit Indo-Aryan Indus-Valley language. The lahnda and Kashmiri appear to be its cognate sister with a common Dardic element in them all"
Mr. Sirajul Haque Memon does not agree either with Dr. Trumpp or with Dr. N.A.Baloch. According:
"Sindhi is one of the Dravidian language, and has its roots in the civilization of Mohen-jo-Daro."
The excavations of Mohen-jo-Daro have opened a new chapter for the study of the origin and ancestry of Sindhi language. It has been agreed upon by all the scholars, archaeologists, historians and anthropologists that Indus Valley was occupied by a Non-Aryan (Dravidian) people before the Aryan settlement in the Indus Valley. They had a very rich culture and a language of their own. The Scandinavian scholars, having tried to decipher the script of Mohen-jo-Daro seals, consider it a proto-Dravidian language, and state:
"The language (that of Mohen-jo-Daro) is a nearly form of Dravidian, called by us proto-Dravidian'. It appears to be very close to the south-Dravidian, especially Tamil, and decidedly younger than the parent language of all Dravidian tongues."
After deep study of Sindhi phonetics, phonology, morphology and syntax, the peculiarities of non-Aryan origin have been observed in Sindhi, and these non-Aryan peculiarities are similar to those of Dravidian languages. It can, therefore, be said that Sindhi has retained the characteristics of indigenous tongue which was in use in ancient Sindh before Aryan settlements in the area. The name of that language was perhaps 'Saindui'.
This theory finds support in Dr. Trumpp's book, "A grammar of Sindhi language", in which he wrote:
"We shall on the other hand be able to trace out a certain residuum of vocables, which we must allot to an old aboriginal language, of which neither name nor extent is now known to us. But which, in all probability was of the Tatar Stock of languages and spread through-out the length and breadth of India before the irruption of the Aryan race, as all other vernaculars contain a similar non-Aryan residuum of words, which have been already designed as 'provincial' by the old prakrit grammarians."
The report of of the Scandinavian, American & Russian scholars have greatly helped the scholars of linguistics in the study of the structure of Sindhi language.
Their reports also assist the scholars in establishing that Sindhi is a non-Aryan & pre-Aryan language, having its roots in the civilization of Mohen-jo-Daro, and the dialects of Dravidian languages, it has been found that phonetically, phonologically, morphologically and syntactically, Sindhi an Dravidian languages are very close to each other, and have lot of similarities. Many examples in this regard can be given. This is, however, a subject still under research and for the final conclusion by the scholars.
After Aryans had occupied the Indus Valley, their culture, language and religion came into contact with the culture, language and religion of the Indus Valley people, and the amalgam produced a fine blend of culture and language for the people of Sindh.
Many phonetic sounds, phonemes, morphemes, words and phrases were borrowed by the Aryans from the rich language of the people of Mohen-jo-Daro and vice versa.
During he long period of history, Sindhi language has absorbed influence of the old Iranian language during Achamenian and Sassanian rule. This influence was followed by prakrit and pali during Buddhist and Brahman period. After the Arab conquest in eighth century A.D., Sindhi borrowed plenty of words from the Arabic language, which became the official as well as the religious language of Sindh for nearly three hundred years.
Thus during this long period of history, Sindhi borrowed thousands of words and phrases from Persian language. But the existence of words and phrases of the borrowed stock did not or could not influence much the indigenous structure (phonological, morphological and syntactical) of Sindhi. It has thus retained the peculiarities of indigenous language even today, and draws attention of scholars to its origin and old ancestry.

Linguistic Boundaries:
Sindhi is one of the major languages of Pakistan, spoken in the province of Sindh by approximately twenty million people. It is one of the oldest languages of the sub-continent, with a rich culture, vast folklore and extensive literature.

Sindhi has extended its isoglosses beyond the geographical boundaries of the province of Sindh. In Northern Sindh it flows over the north-west into Balochistan province, to the North and North-west into the Punjab and the former Bhawalpur State; on the West it is bounded by the mountain range separating Sindh from Balochistan. This boundary has not been crossed by Sindhi, except in the Southern part of the hilly area of Kohistan. Here in general, the language spoken is Balochi but Sindhi is also found being spoken by a good number of population in the former lasbella State, now a part of Balochistan Province. It is spoken as mother tongue. It has spread its influence still further a field towards the Persian Gulf in the Markran area of Balochitan and is spoken as a first language along with Balochi (Markrani) by a large number of people in jadgal, guwadar, ormara and pasni, and has crossed the Gulf and is spoken in Muskat, Abuzahbi and generally in the coastal region.
In the east and south-east, Sindhi has crossed the Rann of Katch and is spoken by a large number of people in Katch, Gujarat and the peninsula of Kathiawar and sorahtar in India.
In the east, it has influenced the speech of the neighboring part of former Marwar and Jaisalmir states of Rajputana in India.
After the partition of India, numerous Sindhi Hindus migrated from Sindh and settled in Central, Western and Northern part of India.
Sindhi is not only spoken in the Indo-Pakistan sub-continent but it is also spoken by approximately 4,00,000 peoples, as their first languages, in Tanzania, Kenya, Uganda, Congo, South Africa, Madagascar, East Africa & in U.K. U.S.A., and Canada by those who have migrated to U.K., U.S.A., and Canada from Uganda and other countries of the world. It is also spoken in Hong Kong, Singapore, Thailand, Srilanka, and in some other countries in Far-East and South-East-Asia by some traders who have settled there in the first quarter of the nineteenth century or even earlier than that by their fathers & fore fathers.

Script of Sindhi language
A word about the scripts of Sindhi language would not be out of place. Sindhi is now being written in Arabic Naskh Script, formally adopted by the British in 1853. Sindhi is also written now in Devanagari script in some parts in India. Before the adoption of the present script, Sindhi was being written in a number of different but cognate scripts derived from Devanagari. Historically the first written from of any language in Sindhi is off course the Indus Script, presently being deciphered by different scholars of the world.
In the Arab period we hear from Ibn Nadeem and Alberuni that Sindhi was being written in 'many' scripts. The earliest evidence of the proto-Devanagari script has been excavated from Bhambhore and Brahmanabad. Only a few Sindhi words are extant on pieces of broken pottery found these mounds. Later we are told by Sir Grierson in his "Linguistic Survey of India" Vol:viii, that Sindhi was at a more recent time written in more than eight different scripts namely Thatta, Khudavadi, luhanki, Khojki, Devanagari,Gurmukhi and Hattai etc. Sir Grierson has given specimen of all such scripts.
To achieve universality in writing for spreading education and in view of the majority of the population being Muslims having an acquaintance with Arabic Naskh script was adopted with slight modifications of letters to suit typical Sindhi sounds, not found in most other languages of the world.