Batticaloa (Tamil: மட்டக்களப்பு, Maṭṭakkaḷappu, IPA: [mɐʈːɐkːɐɭɐpːɯ]; Sinhala: මඩකලපුව, Maḍakalapuwa, IPA: [məɖəkələpuʋə]) is a major city in the Eastern Province, Sri Lanka, and its former capital. It is the administrative capital of the Batticaloa District. The city is the seat of the Eastern University of Sri Lanka and is a major commercial centre. It is on the east coast, 111 kilometres (69 mi) south of Trincomalee, and is situated on an island. Pasikudah is a popular tourist destination situated 35 km (22 mi) northwest with beaches and flat year-round warm-water shallow-lagoons.

Batticaloa is a Portuguese derivation. The original name of the region being the Tamil "Matakkalappu" (translation: Muddy Swamp). According to Mattakallappu Manmiyam (மட்டக்களப்பு மான்மியம்) the word Mattakkallpu consists Tamil words "Mattu" (மட்டு) Matta-derived from "Mattam" (மட்டம்) means 'flat' and geographical name KaLappu. Mukkuwa named this place as KaLappu-Mattam or boundary of lagoon later it became Matta-Kallappu or Flat Lagoon. Also, Batticaloa has a nickname, "Land of the singing fish" (Tamil: மீன் பாடும் தேன் நாடு) due to musical sounds that related to fish or aquatic creature in the Batticaloa Lagoon near the Kallady Bridge. BBC Radio 4 was able to record the mysterious sound in Batticaloa Lagoon. The sound was broadcast by Sri Lanka Broadcasting Corporation in 1960s with the help of Rev. Fr. Lang, a Catholic priest.

Batticaloa is in the eastern coast of Sri Lanka on a flat coastal plain boarded by the Indian Ocean in the east occupies a central part of the eastern Sri Lanka. Its average elevation is around 5 m (16 ft). Batticaloa district has three lagoons such as Batticaloa Lagoon, Valaichchenai Lagoon, and Vakari (Panichchankerni) Lagoon. Among these lagoons, Batticaloa Lagoon is the largest lagoon, which is 56 km (35 mi) long and has an area of 162 km² (63 sq mi), extending from Pankudaweli in North and Kalmunai in South.

There are several islands within the Batticaloa Lagoon such as Puliayantheevu, Buffaloa Island and Bone Island. Many bridges are built across the lagoon connecting the landmasses and the islands. The Puliayantheevu is the metropolitan place of the city. The biggest bridge of all is Lady Manning bridge located at Kallady, which is the main access path to the city from the southern places of the district. This bridge is also famous for Singing fishes which were considered as musical sounds heard in the Kallady lagoon on a full moon day. A priest named Father Lang recorded this musical charm and broadcast it in the 1960s over the (Sri Lanka Broadcasting Cooperation)

Batticaloa beaches are sandy and located along 4 km (2.5 mi) shoreline in the city and further extend through the neighboring places. They include Kallady beach, Pasikudah, and Kalkudah. Pasikudah is a bay protected from the ocean, with a flat and sandy bed extending 150–200 m (490–660 ft) meters from the shore.

Batticaloa has a tropical monsoon climate (Am) under the Köppen climate classification, also generically referred to as 'dry-monsoonal climate'. Batticaloa's climate is warm to hot throughout the year. From March to May, the warmest time of the year, the maximum temperature averages around 32 degrees Celsius (88 degrees Fahrenheit). During the monsoon season from November to February heavy rains are recorded, with average temperature of 25 °C (77 °F). Average annual rainfall in Batticaloa is 1,650.9 mm (65.00 in).

Two main monsoon systems influence the area The Northeast Monsoon வடகிழக்குப் பருவமழை ( November–February), which brings the majority of annual rainfall and occasional flooding.The Southwest Monsoon தென்மேற்கு பருவமழை (May–September), which has a weaker effect but can still produce intermittent showers.

Mattakallappu Manmiyam refers (மட்டக்களப்பு மான்மியம்) Mukkuva or Mutkuhar are known as the first people migrated to this land and constructed seven villages in various areas. They immigrated their people from India and established the kingdom of Mukkuva. The name of the villages and towns in Batticaloa still holds the historical evidence of the ancient batticaloan people. When Mutkuhar intruded through the salty water and reached the destination of their voyage at the forests situated around the lagoon. When they finished. The name given by the Mukkuva was "Kallpu-Mattam" which literally means "boundary of lagoon". Later it was called "Matta-Kallappu" which indicates the destination of Mukkuva's voyage and the water is flat.