The cigar box guitar is a simple chordophone that uses an empty cigar box as a resonator. The earliest had one or two strings; modern models typically have three or more. Generally, the strings are connected to the end of a broomstick or a 1 x 3 inch wood slate and to the cigar box resonator.
Cigars were packed in boxes, crates, and barrels as early as 1800, but the small boxes that we are familiar with today did not exist prior to around 1840. Until then, cigars were shipped in larger crates containing 100 or more per case. After 1840, cigar manufacturers started using smaller, more portable boxes with 20-50 cigars per box.
Trace evidence of cigar box instruments exists from 1840 to the 1860s. The earliest known illustration of a cigar box instrument is an etching copyrighted in 1876 of two American Civil War soldiers at a campsite, one of whom is playing a cigar box fiddle. The etching was created by illustrator and artist Edwin Forbes, who, under the banner of Frank Leslie's Illustrated Newspaper, worked for the Union Army. The etching was included in Forbes's work Life Stories of the Great Army. In the etching, the fiddle clearly shows the brand "Figaro" on the cigar box.
In addition to the etching, plans for a cigar box banjo were published by Daniel Carter Beard, co-founder of the Boy Scouts of America, in 1884 as part of Christmas Eve with Uncle Enos. The plans, retitled "How to Build an Uncle Enos Banjo", were included in the 1890 edition of Beard's American Boy's Handy Book as supplementary material at the back of the book. These plans omitted the story but still showed a step-by-step description of a playable five-string fretless banjo made from a cigar box.
It would seem that the earliest cigar box instruments would be crude and primitive, but this is not always the case. According to William Jehle, curator of The Cigar Box Guitar Museum and the author of One Man's Trash: A History of the Cigar Box Guitar, the museum acquired two cigar box fiddles built in 1886 and 1889 that seem very playable and well built. The 1886 fiddle was made for an 8-year-old boy and is certainly playable, but the 1889 fiddle has a well-carved neck and slotted violin headstock. The latter instrument was made for serious playing.
Cigar box guitars and fiddles were also important in the rise of jug bands and blues. As most of these performers were black Americans living in poverty, many could not afford a "real" instrument. Using these, along with the washtub bass (similar to the cigar box guitar), jug, washboard, and harmonica, black musicians performed blues during socializations.
The Great Depression of the 1930s saw a resurgence of homemade musical instruments. Times were hard in the American South, and sitting on the front porch singing away the blues was a popular pastime. Musical instruments were beyond the means of most people, but with an old cigar box, a piece of broom handle and a couple of wires from the screen door, a guitar was born.
A modern revival of these instruments (also known as the Cigar Box Guitar Revolution) has been gathering momentum with an increase in the number of cigar box guitar builders and performers. A loose-knit group of underground musicians tour the East Coast of the United States each summer under the banner "Masters of the Cigar Box Guitar Tour." These musicians include Doctor Oakroot, Johnny Lowebow, Tomi-O and many others. A growing number of primitive luthiers are adding cigar box guitars to their items for sale. The Top cigar box guitar builders of today are Shane Speal, Mike Snowden, Del Puckett and Peter Lake of Heavy Fog Guitars.
The modern revival is sometimes due to interest in jug bands and the DIY culture, as a cigar box is inexpensive in comparison with other factors, such as strings and construction time. Many modern cigar box guitar makers can be seen as practitioners of a type of lutherie and implement various personal touches, such as the addition of pickups and resonator cones.
The modern revival of cigar box guitars is documented in the 2008 film "Songs Inside the Box", which was shot primarily at the Cigar Box Guitar Extravaganza, an annual event held in Huntsville, Alabama. 
The Cigar Box Guitar Museum, a free display dedicated to cigar box guitars, is located in Speal's Tavern, a small blues club in New Alexandria, Pennsylvania. It is curated by cigar box guitarist Shane Speal and contains over 60 antique and modern cigar box guitars.
Many different tunings can be used for cigar box guitars. Common tunings are:
So I went ahead and made me a guitar. I got me a cigar box, I cut me a round hole in the middle of it, take me a little piece of plank, nailed it onto that cigar box, and I got me some screen wire and I made me a bridge back there and raised it up high enough that it would sound inside that little box, and got me a tune out of it. I kept my tune and I played from then on.-- Lightnin' Hopkins