Presented are results from the recent jet fragmentation and underlying event structure studies carried out by the CDF Collaboration. Multiplicities of charged particles in quark and gluon jets are measured and their ratio is compared to pQCD predictions. The results are compared to the earlier measurements obtained at e⁺ e^- colliders. Average charged particle multiplicities and energy flow in the underlying event are compared to PYTHIA Monte Carlo event generator; the necessary tuning of PYTHIA parameters needed to make it match the data is discussed.

PACS numbers: 13.85.Hd, 13,87.Fh