The Harappans used to trade stone, metal and bone etc. within the Indus civilization area.  They did not use metal coins.  Perhaps they do all kinds of exchanges by exchange.  They were familiar with the wheel and solid wheeled vehicles were prevalent in Harappa.  

A two wheeled clay and bronze toy car has been found from Mohenjodaro and a four wheeled clay toy car from Chanhudaro.  A big wheel of Alvester stone from Lothal and a wheel of bullock cart have been found on the roads from Banawali.  

They established their commercial settlement in northern Afghanistan, with the help of which their trade with Central Asia was carried on.  Many Harappan seals have been unearthed in Mesopotamian excavations, from which the Harappans seem to have imitated many of the toiletries of Mesopotamian citizens.  

The Harappans had a distant trade in the Lajavard gem (Lapis lazuli).  A seal from Mohenjodaro and a clay made toy boat found at Lothal suggest that the Indus people used mast boats for internal and external trade.

The construction of grandsons and sea trade by boats during the period of Indus civilization is confirmed by the evidence of dockyards found from Lothal.  Mesopotamian inscriptions from around 2350 BC and onwards mention a trade relationship with Meluha.  Meluha is the ancient name of the Indus region. 

 Mesopotamian inscriptions mention two intermediate trade centers – Dilmun and Makan.  Both of them were located between Mesopotamia and Meluha.  Dilmun is identified with Bahrain in the Persian Gulf. 

 In the Sumerian writings of Sargon, Bahrain (Dilmun) is called the land of the rising sun.  Evidence of trade from Mesopotamia by both water and land has been found.  There was little contact with Egypt, but Harappan dolls have been found from there.