Pembrokeshire (/ˈpɛmbrʊkʃɪər, -ʃər/ PEM-bruuk-sheer, -⁠shər; Welsh: Sir Benfro [siːr ˈbɛnvrɔ]) is a county in the south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and otherwise by the sea. Haverfordwest is the largest town and administrative headquarters of Pembrokeshire County Council.

The county is generally sparsely populated and rural, with an area of 610 square miles (1,600 km²) and a population of 123,400. After Haverfordwest, the largest settlements are Milford Haven (13,907), Pembroke Dock (9,753), and Pembroke (7,552). St Davids (1,841) is a city, the smallest by population in the UK. Welsh is spoken by 17.2 percent of the population, and for historic reasons is more widely spoken in the north of the county than in the south.

Pembrokeshire's coast is its most dramatic geographic feature, created by the complex geology of the area. It is a varied landscape which includes high sea cliffs, wide sandy beaches, the large natural harbour of Milford Haven, and several offshore islands which are home to seabird colonies. Most of it is protected by Pembrokeshire Coast National Park, and can be hiked on the 190-mile (310 km) Pembrokeshire Coast Path. The interior of Pembrokeshire is relatively flat and gently undulating, with the exception of the Preseli Mountains in the north.

There are many prehistoric sites in Pembrokeshire, particularly in the Preseli Mountains. During the Middle Ages several castles were built by the Normans, such as Pembroke and Cilgerran, and St David's Cathedral became an important pilgrimage site. During the Industrial Revolution the county remained relatively rural, with the exception of Milford Haven, which was developed as a port and Royal Navy dockyard. It is now the UK's third-largest port, primarily because of its two liquefied natural gas terminals. The economy of the county is now focused on agriculture, oil and gas, and tourism.

The county town is Haverfordwest. Other towns include Pembroke, Pembroke Dock, Milford Haven, Fishguard, Tenby, Narberth, Neyland and Newport. In the west of the county, St Davids is the United Kingdom's smallest city in terms of both size and population (1,841 in 2011). Saundersfoot is the most populous village (more than 2,500 inhabitants) in Pembrokeshire. Less than 4 per cent of the county, according to CORINE, is built-on or green urban.

There are three weather stations in Pembrokeshire: at Tenby, Milford Haven and Penycwm, all on the coast. Milford Haven enjoys a mild climate and Tenby shows a similar range of temperatures throughout the year, while at Penycwm, on the west coast and 100m above sea level, temperatures are slightly lower.

The county has on average the highest coastal winter temperatures in Wales due to its proximity to the relatively warm Atlantic Ocean. Inland, average temperatures tend to fall 0.5 °C for each 100 metres increase in height.

The air pollution rating of Pembrokeshire is "Good", the lowest rating.