221st Mixed Brigade was a Scottish Home Service formation of the British Army that served under various titles throughout World War I.

It was not included in the Lowland Division with the rest of the TF units from Southern Scotland, but formed an independent brigade in Scottish Coastal Defences.

[1][2] On the outbreak of war on 4 August 1914, the Lothian Brigade of the Territorial Force (TF) mobilised at Edinburgh under Brigadier-General H.F. Kays as part of Scottish Coastal Defences, with the following units under command:[3][4][5][6] attached: Almost immediately (31 August 1914), TF units were authorised to raise 2nd battalions formed from those men who had not volunteered for, or were not fit for, overseas service, together with new volunteers.

Part of their role was physical conditioning to render men fit for drafting overseas, alongside units of the Training Reserve.

[3] On 26 November 1917, 1203rd (Lowland) Battery transferred to 12th Brigade, Royal Field Artillery, which was reforming in 67th (2nd Home Counties) Division.