Indo-Roman trade relations (see also the spice trade and incense road) was trade between the Indian subcontinent and the Roman Empire in Europe and the Mediterranean Sea. Trade through the overland caravan routes via Asia Minor and the Middle East, though at a relative trickle compared to later times, preceded the southern trade route via the Red Sea, which started around the beginning of the Common Era (CE), following the reign of Augustus and his conquest of Egypt in 30 BCE.

The southern route so helped enhance trade between the ancient Roman Empire and the Indian subcontinent, that Roman politicians and historians are on record decrying the loss of silver and gold to buy silk to pamper Roman wives, and the southern route grew to eclipse and then totally supplant the overland trade route. Roman and Greek traders frequented the ancient Tamil country, present day Southern India and Sri Lanka, securing trade with the seafaring Tamil states of the Pandyan, Chola and Chera dynasties and establishing trading settlements which secured trade with the Indian subcontinent by the Greco-Roman world since the time of the Ptolemaic dynasty a few decades before the start of the Common Era and remained long after the fall of the Western Roman Empire.

The Seleucid dynasty controlled a developed network of trade with the Indian Subcontinent which had previously existed under the influence of the Achaemenid Empire. The Greek-Ptolemaic dynasty, controlling the western and northern end of other trade routes to Southern Arabia and the Indian Subcontinent, had begun to exploit trading opportunities in the region prior to the Roman involvement but, according to the historian Strabo, the volume of commerce between Indians and the Greeks was not comparable to that of later Indo-Roman trade.

The Periplus Maris Erythraei mentions a time when sea trade between Egypt and the subcontinent did not involve direct sailings. The cargo under these situations was shipped to Aden:

Aden – Arabia Eudaimon was called the fortunate, being once a city, when, because ships neither came from India to Egypt nor did those from Egypt dare to go further but only came as far as this place, it received the cargoes from both, just as Alexandria receives goods brought from outside and from Egypt.

— Gary Keith Young, Rome's Eastern Trade: International Commerce and Imperial Policy

The Ptolemaic dynasty had developed trade with Indian kingdoms using the Red Sea ports. With the establishment of Roman Egypt, the Romans took over and further developed the already existing trade using these ports.

Classical geographers such as Strabo and Pliny the Elder were generally slow to incorporate new information into their works and, from their positions as esteemed scholars, were seemingly prejudiced against lowly merchants and their topographical accounts. Ptolemy's Geography represents somewhat of a break from this since he demonstrated an openness to their accounts and would not have been able to chart the Bay of Bengal so accurately had it not been for the input of traders. It is perhaps no surprise then that Marinus and Ptolemy relied on the testimony of a Greek sailor named Alexander for how to reach "Cattigara" (most likely Oc Eo, Vietnam, where Antonine-period Roman artefacts have been discovered) in the Magnus Sinus (i.e. Gulf of Thailand and South China Sea) located east of the Golden Chersonese (i.e. Malay Peninsula). In the 1st-century CE Periplus of the Erythraean Sea, its anonymous Greek-speaking author, a merchant of Roman Egypt, provides such vivid accounts of trade cities in Arabia and India, including travel times from rivers and towns, where to drop anchor, the locations of royal courts, lifestyles of the locals and goods found in their markets, and favorable times of year to sail from Egypt to these places in order to catch the monsoon winds, that it is clear he visited many of these locations.