The 15th (Scottish) Infantry Division was an infantry division of the British Army that served during the Second World War. It was raised on 2 September 1939, the day before war was declared, as part of the Territorial Army (TA) and served in the United Kingdom and later North-West Europe from June 1944 to May 1945.

During the 1930s, tensions increased between Germany and the United Kingdom and its allies. In late 1937 and throughout 1938, German demands for the annexation of the Sudetenland in Czechoslovakia led to an international crisis. To avoid war, the British Prime Minister Neville Chamberlain met with German Chancellor Adolf Hitler in September and brokered the Munich Agreement. The agreement averted a war and allowed Germany to annexe the Sudetenland. Although Chamberlain had intended the agreement to lead to further peaceful resolution of issues, relations between both countries soon deteriorated. On 15 March 1939, Germany breached the terms of the agreement by invading and occupying the remnants of the Czech state.

On 29 March, British Secretary of State for War Leslie Hore-Belisha announced plans to increase the part-time Territorial Army (TA) from 130,000 to 340,000 men and double the number of TA divisions. The plan was for existing TA divisions, referred to as the first-line, to recruit over their establishments (aided by an increase in pay for Territorials, the removal of restrictions on promotion which had hindered recruiting, construction of better-quality barracks and an increase in supper rations) and then form a new division, known as the second-line, from cadres around which the divisions could be expanded. This process was dubbed "duplicating". The 15th (Scottish) Infantry Division was to be a second-line unit, a duplicate of the first-line 52nd (Lowland) Infantry Division. In April, limited conscription was introduced. This resulted in 34,500 twenty-year-old militiamen being conscripted into the regular army, initially to be trained for six months before deployment to the forming second-line units. It was envisioned that the duplicating process and recruiting the required numbers of men would take no more than six months. Some TA divisions had made little progress by the time the Second World War began in September; others were able to complete this work within a matter of weeks.

The embryo of the 15th (Scottish) Infantry Division was formed on 26 August 1939, administered by the 52nd Division, and became an independent formation on 2 September 1939. It took control of the 44th, the 45th and the 46th Infantry Brigades. Due to the lack of official guidance, the newly formed formations were at liberty to choose numbers, styles, and titles. The division adopted the number, title, and divisional insignia of their First World War counterpart, the 15th (Scottish) Division. The brigades did likewise. The divisional insignia, the letter 'O' (being the 15th letter of the alphabet), differed slightly from the original, by not including a triangle inside the circle.

On formation, the 44th (Lowland) Infantry Brigade consisted of the 8th Battalion, Royal Scots; the 6th Battalion, King's Own Scottish Borderers; and the 7th Battalion, King's Own Scottish Borderers. The 45th (Lowland) Infantry Brigade comprised the 6th Battalion, Royal Scots Fusiliers; and the 9th and the 10th Battalions, Cameronians (Scottish Rifles). The 46th (Highland) Infantry Brigade had the 10th and the 11th Battalions, Highland Light Infantry; and the 2nd Battalion, Glasgow Highlanders. The division was initially assigned to Scottish Command, and Major-General Roland Le Fanu became the general officer commanding. Le Fanu's prior experience included staff appointments, and he had fought in the 1937 Waziristan campaign. While primarily made up of Scots, recruits were posted to the division from across the United Kingdom, particularly England.

The war deployment plan for the TA envisioned that its divisions would be deployed overseas, as equipment became available, to reinforce the British Expeditionary Force (BEF) that had already been dispatched to Europe. The TA would join regular army divisions in waves as its divisions completed their training, the final divisions deploying one year after the war began. However, during the opening months of the war, the division lacked the required equipment and personnel. September saw the division drained of manpower. Soldiers, aged 19, were reassigned to other formations; the Ministry of Labour allocated other men to essential industries; and medical standards weeded out those considered unfit. The division was initially scattered across southern Scotland without access to training facilities. On 30 September, after the requisition of civilian transport, the division moved to the Scottish Borders, south of Edinburgh, to start training.

In October 1939, the Commander-in-Chief, Home Forces, General Walter Kirke, was tasked with drawing up a plan, codenamed Julius Caesar, to defend the United Kingdom from a potential German invasion. The division's role in this was largely to defend the Edinburgh and Forth areas. It was not until December that the division moved to undertake this role, with the 44th Brigade positioned astride the Firth of Forth. The rest of the division was based around Glasgow, on either side of the Firth of Clyde. On paper, an infantry division was to have seventy-two modern 25-pounder field guns. By November, the divisional artillery comprised just eight First World War-vintage 4.5 inches (110 millimetres) howitzers. By January, this had increased to sixteen 4.5 in (110 mm) howitzers, in addition to eight First World War-era 18-pounder field guns.

In April 1940, the division marched back to the Borders, and used the move as a training exercise. Elements of the division were then used to provide logistical support for units en route to fight in the Norwegian Campaign. On 9 April, following the start of the campaign, the second-line infantry divisions were requested to each form an independent infantry company of 289 volunteers, who would be deployed to Norway. The 15th Division formed No. 10 Independent Company, but it was not deployed. When the campaign ended in failure, the division was ordered to move south into England to make room for the returning troops. This move promoted Kirke to complain that the division was being moved against his wishes, despite the defensive role assigned to it for southern Scotland. The move took the division to Wiltshire, with the intent to intensively prepare for its deployment to France. Following the German invasion of France and the Low Countries, the English east coast was seen as the area most under threat from German invasion. The division then moved to Essex to defend the coast from Harwich, in the north, to Southend-on-Sea, in the south. To prevent a German invasion, including potential tank attacks, the divisional artillery now comprised twelve 4.5 in (110 mm) howitzers, six 18-pounder field guns, and four Ordnance QF 2-pounder anti-tank guns (compared to an establishment of 48). This was roughly on par with the other eight divisions that had been assigned to defend the coast, although the 15th was one of only two that included anti-tank guns. Additional equipment included 47 Boys anti-tank rifles (against an establishment of 361), 63 Universal Carriers (establishment of 140), and 590 Bren light machine guns (establishment of 644). The division co-operated with the forming Local Defence Volunteers, laid landmines, and erected anti-invasion obstacles within its operating area.