Mabie Todd Swallow,  c. 1935

The idea of a single writing instrument incorporating both pen and pencil goes back a long, long way.  Combination dip pens and pencils were already popular in the 18th century, and in the second half of the 19th century numerous ingenious patented designs offered a variety of novel means to retract and extend nibs and nozzles.

Mabie Todd retracting dip pen & pencil, c. 1880

 

Schnell Penselpen, c. 1929

Not surprisingly, there were early fountain pen combinations as well, but their popularity was decidedly limited.  In the United States, however, this changed suddenly at the end of the 1920s when combos became, for a few years at least, all the rage.  What touched off the fad is not entirely clear, though it has often been associated with the introduction of pen industry veteran Julius Schnell's Penselpen -- highly prized today, but a venture that eventually bankrupted Schnell.

Waterman Ripple combo, c. 1930

The majority of combos from this era were from second and third-tier makers, and ranged in quality from quite good to quite bad.  For the most part, top-line makers did not embrace the combo.  Parker, Waterman, and Wahl-Eversharp combos are particularly scarce, and do not appear to have been advertised or catalogued (Waterman's desk set combo excepted).  Sheaffer and Mabie Todd combos are more common, while the scarcity of Conklin's "Ensembles" lies somewhere in between.

Keystone & Beaumel Durabilt combos, early 1930s

All-metal combos were also popular during this era.  Most of these were produced in the New York City area by firms such as Edward Todd, Hicks, and L.T. & Sons, and were often sold by (and bear the retailer marks of) prominent jewelers such as Tiffany, Cartier, et al. 

The vogue for combos did not spread much beyond the United States, so European combinations are not at all common.  There is one sort of Japanese combo that is frequently seen, however, which is a variant of the low-quality novelty jumbo, made chiefly for export.