Sampling and the creation of multiple images at integer multiples of the sampling frequency
Below is an example of two sine waves at 11 Hz and 1 Hz, both sampled with a 10 Hz sampling clock.  The sampled locations are drawn as circles. If you only had the samples, and had no knowledge of any filtering prior to the sampling process, you would not be able to know for certain if the samples came from a 1 Hz analog signal or an 11 Hz analog signal. In fact, any signal at N fs ± 1 Hz for any integer N would produce the same result. (9 Hz, 11 Hz, 19 Hz, 21 Hz, etc).   



Thus, with appropriate analog bandpass filtering prior the sampling, we can directly sample ("undersample") a bandpass signal, as long as we follow Nyquist's criteria that the sampling rate be > 2x the signal bandwidth. Do not confuse bandwidth with highest frequency content!  The sine wave shown for example has 0 bandwidth in that it occupies an infinitely thin line in the spectrum. Actual bandpass waveforms of interest would have some bandwidth based on their modulation content.

What this picture also helps clarify is the increased sensitivity to any sampling clock jitter when performing bandpass sampling.  Note specifically the slope of the red lower frequency signal as compared to that of the blue higher frequency signal in vicinity of the sample locations, and imagine small variations due to clock jitter and how these variations would transform to amplitude error. 

Please see this answer for specific details related to a conceptual understanding of having multiple frequency "images": Aliasing after downsampling