"Pack Up Your Troubles in Your Old Kit-Bag, and Smile, Smile, Smile" is the full name of a World War I marching song, published in 1915 in London. It was written by Welsh songwriter George Henry Powell under the pseudonym of "George Asaf", and set to music by his brother Felix Powell.

It was featured in the American show Her Soldier Boy, which opened in December 1916

Performers associated with this song include Edward Hamilton, the Victor Military Band, James F. Harrison, Murray Johnson, Reinald Werrenrath, and the Knickerbocker Quartet.
A later play presented by the National Theater recounts how these music hall stars rescued the song from their rejects pile and re-scored it to win a wartime competition for a marching song. It became very popular, boosting British morale despite the horrors of that war. It was one of a large number of music hall songs aimed at maintaining morale, recruiting for the forces, or defending Britain's war aims. Another of these songs, "It's a Long Way to Tipperary", was so similar in musical structure that the two were sometimes sung side by side