The Klasies River Caves are a series of caves located east of the Klasies River Mouth on the Tsitsikamma coast in the Humansdorp district of Eastern Cape Province, South Africa. The Klasies River Main (KRM) site consists of 3 main caves and 2 shelters located within a cliff on the southern coast of the Eastern Cape. The site provides evidence for developments in stone tool technology, evolution of modern human anatomy and behavior, and changes in paleoecology and climate in Southern Africa based on evidence from plant remains.

Klasies River Cave is located on the border of the Tsitsikamma mountain range on the southeastern coast of Africa. The site sits within the Greater Cape Floristic region, characterized by the fynbos biome; however the Klasies River Cave environment is mixed woods and shrubby brushland and maintains a temperate climate. Klasies River main site is located on a sandstone cliff less than 1 kilometer from the Klasies River mouth and on the coast of the Indian Ocean. The district receives approximately 500–700 mm (20–28 in) of rainfall annually.

The site consists of Caves 1 and 2, and the protected overhangs of Cave 1A and 1B, together known as Klasies River main site. However, Cave 2 was not accessible until later stages after there had been significant deposition and build-up of sediments, and Cave 1B has been under-documented; most finds therefore come from Caves 1 and1A. These caves contain 21 meters of deposits that researchers have struggled to delineate stratigraphically. While sea levels fluctuated over time, during certain occupations, the proximity to the coast and the surrounding grasslands provided marine life and terrestrial animals that were exploited by the caves inhabitants.

From 1967–1968 John Wymer and Ronald Singer conducted excavations that revealed evidence of Middle Stone Age (MSA)-associated human habitation beginning approximately 125,000 years ago. Singer and Wymer excavated Caves 1, 1A and 1B, and part of Cave 2; using culture stratigraphy, they determined stages as MSA I, MSA II, Howiesons Poort, MSA III and MSA IV, which allowed comparison across the caves. Critiques of the original excavation include sampling bias due to excavation and screening methods, and combination of stratigraphic layers that obscures the sites' complexity; certain strata were lumped together making it difficult to differentiate between activities at the site and combining artifacts and bones from multiple different strata.

These initial findings prompted successive excavations to examine the varied and complex stratigraphy. Hilary Deacon began work in Caves 1, 1A and 1B from 1984–1995 focusing on the arbitrary delineation (the "Witness Baulk") that Singer and Wymer used to differentiate Cave 1A from Cave 1, as these caves are actually continuous. While the Singer and Wymer excavation used units that were excavated uniformly across the cave layer by layer, successive excavations focused on different stratigraphic approaches. Deacon's excavations maintained the microstratigraphy of the site. Deacon excavated units one by one, independently of other units in the cave, recording the stratigraphy observed in each individual unit before grouping units together based on their shared stratigraphic patterns. Rather than use culture stratigraphy, Deacon used a hybrid strategy combining Singer and Wymer's culture stratigraphy and lithostratigraphy. He developed a descriptive naming pattern for the observed soils instead of Singer and Wymer's classification system, however both systems are still used today.

Sarah Wurz began directing excavations at the site in 2013 and continues today with a continued focus on microstratigraphy; her work is mainly within the Cave 1 Witness Baulk, a section that hadn't been excavated previously. The current work is focused on gathering data from the microstratigraphy and refining the process of micro-scale excavations. This data allows comparison of KRM to other sites across the continent.

The dates of the KRM stratigraphy have been obtained through isotopic analysis and dating of biological materials. Because the site exceeds 50,000 years old, radiocarbon dates are less useful due to carbon contamination. Researchers have resorted to analysis of unstable isotopes, such as Uranium-Thorium (U-Th) to provide more accurate date ranges. Marine isotope stages (MIS) are used to compare large-scale global temporal comparisons; each stage in the Klasies River Caves site correlates with a MIS stage.^{[citation needed]}

The stratigraphy of the site consists of very fine, thin layers of sediment that have compressed under the successive layers on top of them. Researchers have used microstratigraphic techniques to analyze and interpret the complex timeline of sediment deposition and post-depositional activities within the caves. Because the cave system has so many varied layers and the different caves have different depositional characteristics and sediment properties, it has been hard to create a uniform system to group and chronologically group the layers for a site-wide comparison; natural processes such as erosion, and the influence of people at certain areas of the site (anthropogenic deposition of shell middens, hearths, etc.) have further complicated the interpretation of the stratigraphy. A lithostratigraphic and culture stratigraphic approach are both used at KRM today.^{[citation needed]}