Porth (Welsh: Y Porth) is a town and community in the county borough of Rhondda Cynon Taf, within the historic county boundaries of Glamorgan, Wales. Lying in the Rhondda Valley, it is regarded as the gateway connecting the Rhondda Fawr and Rhondda Fach valleys due to both valleys meeting at Porth. The Welsh word "porth" means "gate". Porth is a predominantly English-speaking community.

Neighbouring villages include Trealaw, Trebanog, Trehafod and Ynyshir.

During prehistoric times the area now known as Porth was an uninhabited wooded area. Although there is evidence of settlements in the upper reaches of the valley, only cairns used as way-markers have been discovered on the higher points in the Porth area. During the medieval period the area came under the commote of Glynrhondda within the cantref of Penychen, though the area remained uninhabited. Although there were no permanent buildings of note at this time, it is known that the area would have experienced travelers with two bridges built over the River Rhondda at Porth, the Pont Rheola and Pont y Cymmer. Both bridges date to at least the 1530s when they were mentioned by antiquary John Leland. These bridges were wooden in construct and were later rebuilt in stone. The first buildings of note in the region were built to the south of Porth in the community known today as Cymmer, mainly a chapel, Capel y Cymmer (1743) and a mill on the south bank of the River Rhondda. By the 18th century there were a handful of farm houses, mainly in the northern slopes of Llwyncelyn. During this pre-industrial era, the locale was known as Cymmer, an old Welsh word that describes the point where two rivers converge. It was only during the industrial period that the mining operations of the Porth Estate and the subsequently named railway station that saw the name Porth adopted.

In 1809, Walter Coffin sunk the first coal pit in the Rhondda, further up the valley in Dinas, but a lack of a transportation network greatly affected the profitability of coal mining as an industry in the region. Coffin tackled this problem by constructing a one-mile tramline which connected his mines in Dinas to a tramline built by Dr. Richard Griffiths at Denia (modern spelling Dynea) (Pontypridd), which linked to a private canal that joined onto the Glamorganshire Canal at Treforest. Coffin's tramline followed the southern bank of the River Rhondda and ran through Porth. The existence of the tramline made the development of the Porth and Cymmer region far more attractive, and by the middle of the 19th century there was an impetus to expand coal mining in the area. In 1841 Richard Lewis joined Coffin in trying to exploit the region with his level built at Cymmer. This resulted in the construction of around fifty miners' cottages, several of which were located in Porth. In 1844 Lewis Edwards of Newport and George Gethin of Penygraig opened a small level at Nyth-bran on the eastern borders of Porth, the villages' first coal mine. This was followed in 1845 by the sinking of the Porth Colliery by David James of Merthyr, the success of which saw him build the Llwyncelyn Colliery in 1851, also in Porth. By 1850 the Taff Vale Railway had been extended to Cymmer replacing the tramline, allowing direct access between the lower Rhondda and the ports of Cardiff.

In 1850 the Troedyrhiw Colliery (later to become the Aber-Rhondda Colliery), which was sunk on the northern borders of Porth and the neighbouring village of Ynyshir by Leonard Hadley of Caerleon five years earlier, came into the ownership of a new consortium known as the Troedyrhiw Coal Company. This company was formed by James Thomas, a former miner, Matthew Cop, a Cardiff docksman and John Lewis, a grocer from Aberdare. In 1852 the same company opened the Tynewydd Colliery at the junction of the Rhondda Fawr and Fach rivers, Porth's fourth mine. The mine quickly struck the Rhondda No. 3 seam, and coking ovens were built at the surface, providing further employment.

With the increase in population, transport links began to improve in the Rhondda. This was hampered by subsidence caused the mining underground, which resulted in the roads of Porth Square sinking by eight foot. In 1860 a two horsed omnibus service was introduced between Porth and Pontypridd, but was replaced by a system of horsedrawn tramcars in 1888. Although the tramline and subsequently the railway had passed through Porth for two decades, servicing the collieries, it was not until 1861 that the village had its first railway station; and a passenger service did not commence until January 1863.

As the population continued to increase, businesses and infrastructure grew around the coal industry. The Rhondda Urban Council chose Porth as one of two sites to build gas works and the area around Porth Square and Hannah Street became the commercial centre of the village. One of the more notable businesses to open in Porth was the Thomas & Evans grocers one of the first of a chain of shops owned by William Thomas and William Evans two entrepreneurs from Pembrokeshire. Evans became an important figure in the growth of Porth, and in the late 1890s he opened a jam factory and the Welsh Hills Mineral Water factory, later to become Corona carbonated drinks which would remain a major manufacturer within the village up until the 1980s.

Coal mining in the Rhondda continued to expand throughout the early 20th century, although no further mines were sunk in Porth. The population continued to grow but conditions became hard after the Great Depression, and by the mid 1920s unemployment among mine workers rocketed. Matters worsened after the disastrous general strike of 1926 which saw many miners out of work for months. As mechanisation allowed other mining areas to become more profitable, the antiquated Rhondda mines sunk nearly 75 years earlier were unable to modernise and one-by-one began to close. Porth, like the rest of the Rhondda, was built solely around the coal industry, and with its collapse came mass unemployment, resulting in economic migration. There was a brief respite during the Second World War, when employment rose sharply. This was partially due for a need for Rhondda steam coal, but also due to large munition factories built in Bridgend, Hirwaun and Treforest to which the workers commuted. With the end of the war it was apparent that unemployment would return, but to ensure that the newly found factory skills gained during the previous six years were not lost the British Government passed the Distribution of Industry Act in 1945. This saw 25 new industry come to the Rhondda, six of them based in Porth. They ranged from Messrs. Jacob Beatus' box making company, a metal toy factory and a branch of Remploy aimed at disabled workers.