From worst-hit Aceh province in Indonesia to the tourist beaches of Thailand and tropical Sri Lanka, thousands of survivors, victims' relatives and officials held on Monday a minute's silence at the time the waves hit, as part of commemoration ceremonies.
On 26 December 2004, a magnitude-9 earthquake ruptured the sea floor off Indonesia's Sumatra island, sending 10-metre-high waves roaring across the Indian Ocean at jetliner speeds that crashed into seaside communities in a dozen countries.
The disaster's scale was overwhelming.
At least 216,000 people were killed or disappeared in the waves, with the UN putting the number of the dead at 223,000, although it says some countries are still updating their figures.
The true toll will probably never be known - many bodies were lost at sea, and in some cases the populations of places struck were not accurately recorded.
Indonesia: 131,338 dead; 25,016 missing
Sri Lanka: 31,229 dead; 4093 missing
India: 10,749 dead; 5640 missing
Thailand: 5395 dead; 2817 missing
Somalia: 289 dead and missing
Myanmar: 90 dead; 10 missing
Maldives: 82 dead; 26 missing
Malaysia: 68 dead
Tanzania: 11 dead
Bangladesh: 2 dead
Seychelles: 2 dead
Kenya: 1 dead
Sources: Government agencies, United Nations
The day's solemn commemorations began in Indonesia, where President Susilo Bambang Yudhoyono led an emotional ceremony with a minute's silence to remember the 168,000 people killed in his country's ravaged Aceh province.
"Let us now bow our heads in silence to pray for the souls of hundreds of thousands who lost their lives," he said on the outskirts of Banda Aceh near the Ulee Lheu mosque, the only building left standing in the obliterated area.
People prayed at mass graves for children swept away by the tsunami, walked on beaches battered by the waves and attended prayers at mosques, temples and churches.
Darmawati, 39, who lost her husband, two daughters and both her parents in the disaster, said: "It is important for me to come here to pray for my family, may they rest in peace.
"I pray that God will give me strength to raise my only son that survived," she added, breaking down in tears at a mass prayer in the Acehnese village of Kajhu.
Susilo Yudhoyono (L) expressed
tearful emotion at one ceremony
Thousands of homes and livelihoods were destroyed - entire villages and parts of the Indonesian city of Banda Aceh were wiped off the map - and more than two million people left as refugees.
In southern Thailand, where about 5400 Thais and foreign holidaymakers were killed, mourners signed books of remembrance, or tossed flowers into the sea as they gathered along the battered beaches where their loved ones died.
In Bang Nieng, hundreds mourned in the shadow of a police patrol boat that was washed one kilometre inland by the waves, and now stands as a memorial to the catastrophe.
"One year has passed, we continue the rebuilding process. Much progress has been made but we have more to do still. Our work is not over," said Somkid Jatusripitak, the Thai deputy prime minister.
India, Sri Lanka
In India, where more than 10,700 people were killed and 5600 others are listed as missing, survivors also offered tearful tributes.
The worst-hit district in the southern state of Tamil Nadu, where almost 6000 people died, observed a minute's silence at the moment the waves slammed into the shore there.
A minute of silence in Tamil Nadu
where almost 6000 people died
In some villages trees were planted for each of the dead, while in others lamps and candles were lit and religious services and beachside ceremonies were held.
On the palm-fringed island of Car Nicobar, India's military unveiled a memorial while women thronged Nicobar's once-fabulous beaches to pray to their gods for the sea to remain calm. Priests called on villagers to gather at the still-standing churches in remembrance of those who died.
Sri Lanka will pay tribute to an estimated 31,000 people killed there by the tsunami with a two-minute silence and coast-to-coast candlelight vigils.
The tsunami generated one of the most generous outpourings of foreign aid.
Mourners from all over the world
gathered at tsunami-hit sites
Some $13 billion was pledged to relief and recovery efforts, the UN says, of which 75% has already been secured.
But the pace of relief and reconstruction has been criticised, and frustration has grown among some of the 80% of refugees who are still living in tents, plywood barracks or the homes of family and friends.
The tsunami resulted in a ceasefire between the government and fighters in Aceh that ended a decades-old separatist conflict.
But hopes of a similar end to Sri Lanka's long-running civil conflict were dashed in an atmosphere of bickering over aid delivery and an upsurge in violence since the disaster.