Samantha Louise Lewthwaite (/ˈluːθweɪt/; born 5 December 1983), also known as Sherafiyah Lewthwaite or the White Widow, is a British terrorist and suspected mass murderer who is one of the Western world's most wanted terrorism suspects. Lewthwaite, the widow of 7/7 London terrorist bomber Germaine Lindsay, is accused of causing the deaths of more than 400 people. She is a fugitive from justice in Kenya, where she is wanted on charges of possession of explosives and conspiracy to commit a felony and is the subject of an Interpol Red Notice requesting her arrest with a view to extradition.

Lewthwaite is alleged to be a member of the Somalia-based radical Islamic militant group Al-Shabaab. She is accused of orchestrating grenade attacks at non-Muslim places of worship, and is believed to have been behind an attack on those watching football in a bar in Mombasa during Euro 2012. In September 2013, there was speculation over her possible involvement in the Nairobi Westgate shopping mall attack, although other reports cast doubt on this, or said her role had been exaggerated. She was dubbed the "White Widow" by the news media, a play on words referencing her race and the death of her first husband and the practice of referring to Chechen female suicide bombers as "black widows".

Lewthwaite was born to parents Andrew and Elizabeth Christine (née Allen) Lewthwaite in Banbridge, County Down in 1983. Her father is a former British Army soldier who served in the 9th/12th Royal Lancers and had met her mother while he was stationed in Northern Ireland in the 1970s. Following her birth the family lived for a short period in Northern Ireland, where her father worked as a lorry driver, before settling in Aylesbury, England. She attended Elmhurst middle school and The Grange secondary school in Aylesbury. She studied for a politics and religion degree at the School of Oriental and African Studies, University of London, but dropped out.

Lewthwaite's parents separated in 1994, and friends later reported that she was badly affected by the break-up and sought solace from Muslim neighbours who she believed had a stronger family network. Born as a Christian, by the age of 17 she had converted to Islam. She adopted the name Sherafiyah at the time of her conversion.

She met Germaine Lindsay on the Internet and arranged to meet him at a Stop the War march in Hyde Park, London; they married in Aylesbury on 30 October 2002, using the Islamic names Asmantara and Jamal. Lewthwaite's parents, who "never came to terms with their daughter's conversion", refused to attend the ceremony.

Three years later, at 8:50 a.m. on 7 July 2005, Lindsay blew himself up on a train travelling between King's Cross and Russell Square tube stations. He killed 26 civilians in his suicide attack. Lewthwaite was eight months pregnant with their second child, a daughter, at the time of his death, and their first child, a son, was 14 months old. Lewthwaite reported her husband missing six days after the bombing by telephoning a helpline set up for families of the victims. She denied prior knowledge of the attacks and said:

I totally condemn and am horrified by the atrocities. I am the wife of Germaine Lindsay, and never predicted or imagined that he was involved in such horrific activities. He was a loving husband and father. I am trying to come to terms with the recent events. My whole world has fallen apart, and my thoughts are with the families of the victims of this incomprehensible devastation.

She was placed in protective custody in a police 'safe house' after an attempt to set fire to her home in the immediate aftermath of the bombings. At the inquest into the bombings, it was disclosed that Lewthwaite had associated with Mohammad Sidique Khan, the ringleader of the London bombers, before the attacks.