A grandfather shirt or grandad shirt is a long-sleeved or short-sleeved flannel or brushed cotton band collared shirt. Traditional shirts are white with coloured vertical stripes. Longer shirts are used as nightshirts or pajamas. The nightshirt version can include a matching nightcap.

The style of shirt (called a union shirt) was also worn by working-class men in the United Kingdom during the industrial era. At this period, the lack of a turndown or collar "cape" was filled by the use of a detachable collar. The 2010s decade has also seen the garment feature as a mainstream fashion item for men.^[1]

The grandfather shirt is also made of Irish linen. The linen version is colloquially known as a 'Sunday shirt'. Sunday shirts are often paired with black trousers or Irish tweed pants and worn to mass, christenings, funerals, and weddings.

In popular culture, a variety of traditional Irish clothing was featured on the BBC series Ballykissangel and the Irish folk band, The Clancy Brothers were often photographed wearing traditional Irish clothes.

A similar collarless shirt or tunic, known as a kurta, is traditionally worn in the Islamic world and South Asia. This usually has three or four buttons, and is often decorated with intricate embroidery.