The town of Bangkok began as a small trading center and port community on the west bank of the Chao Phraya River serving the Ayutthaya Kingdom, the precursor of modern Thailand which existed from 1350 to 1767. It is believed that the town's name derived from either Bang Makok, bang being the Central Thai name for towns or villages situated on the bank of a river, and makok  being the Thai name of either Spondias pinnata, Spondias mombin or Elaeocarpus hygrophilus (plants producing olive-like fruits), or Bang Koh, koh meaning "island," a reference to the area's landscape which was carved by rivers and canals.

After the fall of Ayutthaya to the Burmese Kingdom in 1767, the newly declared King Taksin established a new capital in the area of then-Bangkok, which became known as Thonburi. When Taksin's reign ended in 1782, King Buddha Yodfa Chulaloke reconstructed the capital on the east bank of the river and gave the city a ceremonial name (see below) which became shortened to its current official name, Krung Thep Maha Nakhon (which means "city of angels"). The new city, however, also inherited the name Bangkok, which continued to be used by foreigners to refer to the entire city and became its official English name, while in Thai the name still refers only to the old district on the west bank of the river. The city has since vastly modernized and undergone numerous changes, including the introduction of transportation and utility infrastructure in the reigns of King Mongkut and King Chulalongkorn, and quickly developed into the economic center of Thailand.

The full ceremonial name of the city given by King Buddha Yodfa Chulaloke, and later edited by King Mongkut, is Krung Thep Mahanakhon Amon Rattanakosin Mahinthara Yuthaya Mahadilok Phop Noppharat Ratchathani Burirom Udomratchaniwet Mahasathan Amon Piman Awatan Sathit Sakkathattiya Witsanukam Prasit listen (help·info)). This ceremonial name is composed in combination of two ancient Indian languages, Pāli and Sanskrit. According to the romanisation of these languages, it can actually be written as Krung-dēvamahānagara amararatanakosindra mahindrayudhyā mahātilakabhava navaratanarājadhānī purīrāmasya utamarājanivēsana mahāsthāna amaravimāna avatārasthitya shakrasdattiya vishnukarmaprasiddhi. It translates to "The city of angels, the great city, the eternal jewel city, the impregnable city of God Indra, the grand capital of the world endowed with nine precious gems, the happy city, abounding in an enormous Royal Palace that resembles the heavenly abode where reigns the reincarnated god, a city given by Indra and built by Vishnukam".

Local school children are taught the full name, although few can explain its meaning because many of the words are archaic, and unknown to all but a few. Most Thais who do recall the full name do so as a result of its use in a popular song, Krung Thep Mahanakhon (1989) by Asanee-Wasan Chotikul and will often recount it by recalling the song at the same time, much in the same way that English speakers might sing the alphabet song while reciting the English alphabet.

The full name of the city is listed by Guinness Book of Records as the world's longest place name.^[2]

The Bangkok special administrative area covers 1,568.7 km², making it the 68th largest province in Thailand. Much of the area is considered the city of Bangkok, therefore making it one of the largest cities in the world.^{[citation needed]} The Chao Phraya River, Thailand's longest river which stretches 372 km, is Bangkok's main geographical feature. The Chao Phraya River basin, the area surrounding Bangkok, and the nearby provinces comprise a series of plains and river deltas that lead into the Bay of Bangkok about 30 km south of the city center. This gave rise to Bangkok's appellation as the "Venice of the East" due to the number of canals and passages that divide the area into separate patches of land. The city once used these canals, which were plentiful within Bangkok itself, as divisions for city districts. However, as the city grew in the second half of the 20th century, the plan was abandoned and a different system of division was adopted.

Bangkok lies about two meters above sea level. This low ground level causes problems for the protection of the city against floods during the monsoon season. Often after a downpour, water in canals and the river overflows the banks, resulting in massive floods. The Bangkok Metropolitan Administration (BMA) has recently installed higher planks alongside some canals to keep water levels from reaching street level. There are however some downsides for Bangkok's extensive canal routes, as the city is rumored to be sinking an average of two inches a year as it lies entirely on a swamp.^{[citation needed]} Some reports say that the city is sinking as much as four inches a year, and this combined with the rising sea level will leave Bangkok under 50 cm to 100 cm of water by 2025.^{[citation needed]}

Bangkok has a tropical monsoon climate under the Köppen climate classification system. Bangkok is said to have the highest average temperature of any city in the world.^{[citation needed]} Average temperatures in the city are about 2°C higher than the ones shown for the Don Muang Airport at 1960-1990 period. Absolute maxima is 40.8°C and absolute minima is 9.9°C. The coldest temperatures were recorded in January 1924, January 1955, January 1974 and December 1999. The coldest daytime maximun temperature was 22.3C recorded in December 1999. Hailstorms are virtually unheard in the city, since it was recorded a single hailstorm in the past 50 years.