It is located between the Indian states of Maharashtra to the north and Karnataka to the east and south, with the Arabian Sea forming its western coast. It is India's smallest state by area and its fourth-smallest by population. Goa has the highest GDP per capita among all Indian states, two and a half times as high as the GDP per capita of the country as a whole. The Eleventh Finance Commission of India named Goa the best-placed state because of its infrastructure, and India's National Commission on Population rated it as having the best quality of life in India (based on the commission's “12 Indicators”). It is the third-highest ranking among Indian states in the human development index.

Panaji is the state's capital, while Vasco da Gama is its largest city. The historic city of Margão in Goa still exhibits the cultural influence of the Portuguese, who first voyaged to the subcontinent in the early 16th century as merchants, and conquered it soon thereafter, whereupon Goa became an overseas territory of the Portuguese Empire, part of what was then known as Portuguese India, and remained as such for about 450 years until it was annexed by India in 1961. Goa's official language, which is spoken by a majority of its inhabitants, is Konkani.

Goa is visited by large numbers of international and domestic tourists each year because of its white-sand beaches, active nightlife, places of worship, and World Heritage-listed architecture. It also has rich flora and fauna because it lies very close to the North Western Ghats rainforests, one of the rare biodiversity hotspots of the world.

After the Bahmani-Bijapuri city of Goa was captured by Afonso de Albuquerque in 1510, and made the capital of the Estado da Índia, the city gave its name to the contiguous territories. The origin of the city name Goa is unclear. In ancient literature, Goa was known by many names, such as Gomanchala, Gopakapattana, Gopakapattam, Gopakapuri, Govapuri, Govem, and Gomantak. Other historical names for Goa are Sindapur, Sandabur, and Mahassapatam.

Rock art engravings (petroglyphs) are present on laterite platforms and granite boulders in Usgalimal near the west flowing Kushavati river and in Kajur. In Kajur, the rock engravings of animals, tectiforms and other designs in granite have been associated with what is considered to be a megalithic stone circle with a round granite stone in the centre. Petroglyphs, cones, stone-axe, and choppers dating to 10,000 years ago have been found in various locations in Goa, including Kazur, Mauxim, and the Mandovi-Zuari basin. Evidence of Palaeolithic life is visible at Dabolim, Adkon, Shigao, Fatorpa, Arli, Maulinguinim, Diwar, Sanguem, Pilerne, and Aquem-Margaon. Difficulty in carbon dating the laterite rock compounds poses a problem for determining the exact time period.

Early Goan society underwent radical change when Indo-Aryan and Dravidian migrants amalgamated with the aboriginal locals, forming the base of early Goan culture.

In the 3rd century BC, Goa was part of the Maurya Empire, ruled by the Buddhist emperor, Ashoka of Magadha. Buddhist monks laid the foundation of Buddhism in Goa. Between the 2nd century BC and the 6th century AD, Goa was ruled by the Bhojas of Goa. Chutus of Karwar also ruled some parts as feudatories of the Satavahanas of Kolhapur (2nd century BC to the 2nd century AD), Western Kshatrapas (around 150 AD), the Abhiras of Western Maharashtra, Bhojas of the Yadav clans of Gujarat, and the Konkan Mauryas as feudatories of the Kalachuris. The rule later passed to the Chalukyas of Badami, who controlled it between 578 and 753, and later the Rashtrakutas of Malkhed from 753 to 963.

In 1312, Goa came under the governance of the Delhi Sultanate. The kingdom's grip on the region was weak, and by 1370 it was forced to surrender it to Harihara I of the Vijayanagara Empire. The Vijayanagara monarchs held on to the territory until 1469 when it was appropriated by the Bahmani sultans of Gulbarga. After that dynasty crumbled, the area fell into the hands of the Adil Shahis of Bijapur, who established as their auxiliary capital the city known under the Portuguese as Velha Goa (or Old Goa).

After the Battle of Buxar (1764), the British East India Company obtained the diwani rights (rights to administer and collect tax revenue) for Bihar, Bengal and Odisha. The rich resources of fertile land, water and skilled labour had attracted the foreign imperialists, particularly the Dutch and British, in the 18th century. A number of agriculture-based industries had been started in Bihar by foreign entrepreneurs. Bihar remained a part of the Bengal Presidency of British India until 1912, when Bihar and Orissa were carved out as a separate province.

In 1510, the Portuguese defeated the ruling Bijapur sultan Yusuf Adil Shah with the help of a local ally, Timoji, a privateer. They set up a permanent settlement in Velha Goa. This was the beginning of Portuguese colonial rule in Goa that would last for four and a half centuries, until its annexation by India in 1961. The Goa Inquisition, a formal tribunal, was established in 1560, and was finally abolished in 1812.

In 1843, the Portuguese moved the capital to the Cidade da Nova Goa, today known as Panaji, from Velha Goa. By the mid-18th century, Portuguese expansions lost other possessions in India until their borders stabilised and formed the Goa, Daman and Diu which included Silvassa prior to the Annexation, it was known as Estado da Indìa in Indo-Portuguese, that is the "State of Portuguese India".

On 19 December 1961, the Indian Army invaded with Operation Vijay resulting in the annexation of Goa, and of Daman and Diu islands into the Indian union. Goa, along with Daman and Diu, was organised as a centrally administered union territory of India. On 16 January 1967 a referendum was held in Goa, to decide the future of the Union Territory of Goa, Daman and Diu. It was the only referendum to have been held in independent India. The referendum offered the people of Goa a choice between continuing as a union territory or merging with the state of Maharashtra and the majority chose the former. On 30 May 1987, the union territory was split, and Goa was made India's twenty-fifth state, with Daman and Diu remaining a union territory.

Goa's seven major rivers are the Zuari, Mandovi, Terekhol, Chapora, Galgibag, Kumbarjua canal, Talpona and the Sal. The Zuari and the Mandovi are the most important rivers, interspaced by the Kumbarjua canal, forming a major estuarine complex. These rivers are fed by the Southwest monsoon rain and their basin covers 69% of the state's geographical area. These rivers are some of the busiest in India. Goa has more than 40 estuarine, eight marine, and about 90 riverine islands. The total navigable length of Goa's rivers is 253 km (157 mi). Goa has more than 300 ancient water tanks built during the rule of the Kadamba dynasty and over 100 medicinal springs.

Goa features a tropical monsoon climate under the Köppen climate classification. Goa, being in the tropical zone and near the Arabian Sea, has a hot and humid climate for most of the year. The month of May is usually the hottest, seeing daytime temperatures of over 35 °C (95 °F) coupled with high humidity. The state's three seasons are Southwest monsoon period (June–September), post-monsoon period (October–January), and pre-monsoon period (February–May). Over 90% of the average annual rainfall (3,000 mm or 120 in) is received during the monsoon season.

Equatorial forest cover in Goa stands at 1,424 km2 (549.81 sq mi), most of which is owned by the government. Government-owned forest is estimated at 1,224.38 km2 (472.74 sq mi) whilst private is given as 200 km2 (77.22 sq mi). Most of the forests in the state are located in the interior eastern regions of the state. The Western Ghats, which form most of eastern Goa, have been internationally recognised as one of the biodiversity hotspots of the world. In the February 1999 issue of National Geographic Magazine, Goa was compared with the Amazon and the Congo basins for its rich tropical biodiversity

Goa's wildlife sanctuaries boast of more than 1512 documented species of plants, over 275 species of birds, over 48 kinds of animals and over 60 genera of reptiles.

Goa is also known for its coconut cultivation. The coconut tree has been reclassified by the government as a palm (like grass), enabling farmers and real estate developers to clear land with fewer restrictions.

Rice is the main food crop, and pulses (legume), Ragi (Finger Millet), and other food crops are also grown. Main cash crops are coconut, cashew nut, areca nut, sugarcane, and fruits like pineapple, mango and banana. Goa's state animal is the Gaur, the state bird is the Flame-throated bulbul, and the state tree is the Matti (Asna).

The important forest products are bamboo canes, Maratha barks, chillar barks, and the bhirand. Coconut trees are ubiquitous and are present in almost all areas of Goa barring the elevated regions. A variety of deciduous trees, such as teak, Sal tree, cashew, and mango trees are present. Fruits include jackfruit, mango, pineapple, and "blackberry" ("podkoam" in the Konkani language). Goa's forests are rich in medicinal plants.

Foxes, wild boar and migratory birds are found in the jungles of Goa. The avifauna (bird species) includes kingfisher, myna and parrot. Numerous types of fish are also caught off the coast of Goa and in its rivers. Crab, lobster, shrimp, jellyfish, oysters, and catfish are the basis of the marine fishery. Goa also has a high snake population. Goa has many famous "National Parks", including the renowned Salim Ali Bird Sanctuary on the island of Chorão. Other wildlife sanctuaries include the Bondla Wildlife Sanctuary, Molem Wildlife Sanctuary, Cotigao Wildlife Sanctuary, Madei Wildlife Sanctuary, Netravali Wildlife Sanctuary, and Mahaveer Wildlife Sanctuary.

Goa has more than 33% of its geographic area under government forests (1224.38 km2) of which about 62% has been brought under Protected Areas (PA) of Wildlife Sanctuaries and National Park. Since there is a substantial area under private forests and a large tract under cashew, mango, coconut, etc. plantations, the total forest and tree cover constitutes 56.6% of the geographic area.

Goa's state domestic product for 2017 is estimated at $11 billion at current prices. Goa is India's richest state with the highest GDP per capita – two and a half times that of the country – with one of its fastest growth rates: 8.23% (yearly average 1990–2000). Tourism is Goa's primary industry: it gets 12%of foreign tourist arrivals in India. Goa has two main tourist seasons: winter and summer. In winter, tourists from abroad (mainly Europe) come, and summer (which, in Goa, is the rainy season) sees tourists from across India. Goa's net state domestic product (NSDP) was around US$7.24 billion in 2015–16.

Tourism is generally focused on the coastal areas of Goa, with lower tourist activity inland. In 2010, there were more than 2 million tourists reported to have visited Goa, about 1.2 million of whom were from abroad. As of 2013, Goa was a destination of choice for Indian and foreign tourists, particularly Britons and Russians, with limited means who wanted to party. The state was hopeful that changes could be made which would attract a more upscale demographic.

Goa stands 6th in the Top 10 Nightlife cities in the world in National Geographic Travel. Notable nightclubs in Goa include Chronicle, Mambos and Sinq. One of the biggest tourist attractions in Goa is water sports. Beaches like Baga and Calangute offer jet-skiing, parasailing, banana boat rides, water scooter rides, and more. Patnem beach in Palolem stood third in CNN Travel's Top 20 Beaches in Asia.

Over 450 years of Portuguese rule and the influence of the Portuguese culture presents to visitors to Goa a cultural environment that is not found elsewhere in India. Goa is often described as a fusion between Eastern and Western culture with Portuguese culture having a dominant position in the state be it in its architectural, cultural or social settings. The state of Goa is famous for its excellent beaches, churches, and temples. The Bom Jesus Cathedral, Fort Aguada and a new wax museum on Indian history, culture and heritage in Old Goa are other tourism destinations.

Goa has two World Heritage Sites: the Bom Jesus Basilica and churches and convents of Old Goa. The basilica holds the mortal remains of St. Francis Xavier, regarded by many Catholics as the patron saint of Goa (the patron of the Archdiocese of Goa is actually Saint Joseph Vaz). These are both Portuguese-era monuments and reflect a strong European character. The relics are taken down for veneration and for public viewing, per the prerogative of the Church in Goa, not every ten or twelve years as popularly thought and propagated. The last exposition was held in 2014.

Goa has three important museums: the Goa State Museum, the Naval Aviation Museum and the National Institute of Oceanography. The aviation museum is one of three in India (the others are in Delhi and Bengaluru). The Goa Science Centre is in Miramar, Panaji. The National Institute of Oceanography, India (NIO) is in Dona Paula. Museum of Goa is a privately owned contemporary art gallery in Pilerne Industrial Estate, near Calangute.

Rice with fish curry (xit koddi in Konkani) is the staple diet in Goa. Goan cuisine is famous for its rich variety of fish dishes cooked with elaborate recipes. Coconut and coconut oil are widely used in Goan cooking along with chili peppers, spices, and vinegar, used in the Catholic cuisine, giving the food a unique flavor. Goan cuisine is heavily influenced by Portuguese cuisine.

Goan food may be divided into Goan Catholic and Goan Hindu cuisine with each showing very distinct tastes, characteristics, and cooking styles. Pork dishes such as Vindalho, Xacuti, chouriço, and Sorpotel are cooked for major occasions among the Goan Catholics. A mixed vegetable stew, known as Khatkhate, is a very popular dish during the celebrations of festivals, Hindu and Christian alike. Khatkhate contains at least five vegetables, fresh coconut, and special Goan spices that add to the aroma.

Sannas, Hitt, are local rice cakes and Polle, Amboli, and Kailoleo are rice pancakes; all are native to Goa. A rich egg-based, multi-layered baked sweet known as bebinca is traditional at Christmas.

The most popular alcoholic beverage in Goa is feni. Cashew feni is made from the double distillation of the fermented fruit juice of the cashew tree, while coconut feni is made from the double distillation of the fermented sap of toddy palms. Urrak is another local liquor prepared from the single distillation of the fermented cashew fruit juice. In fact the bar culture is one of the unique aspects of the Goan villages where a local bar serves as a meeting point for villagers to unwind. Goa also has a rich wine culture due to Portuguese rule.

The architecture of Goa is a combination of Goan, Ottoman and Portuguese styles. Since the Portuguese ruled and governed for four centuries, many churches and houses bear a striking element of the Portuguese style of architecture. Goan Hindu houses do not show any Portuguese influence, though the modern temple architecture is an amalgam of original Goan temple style with Dravidian, Hemadpanthi, Islamic, and Portuguese architecture. The original Goan temple architecture fell into disuse as the temples were demolished by the Portuguese and the Sthapati known as Thavayi in Konkani were converted to Christianity though the wooden work and the Kavi murals can still be seen.