The Multiwavelength Approach to Unidentified Gamma-Ray Sources -- Regular Particle Acceleration in Relativistic Jets -- The Converter Mechanism of Particle Acceleration and its Applications to the Unidentified EGRET Sources -- An Examination of Candidate AGN Counterparts to Unidentified EGRET Sources -- A Search for TeV Emission from X-Ray Selected AGN with Milagro -- Beaming Effects in GRBs and Orphan Afterglows -- Pulsar Slot Gaps and Unidentified EGRET Sources -- Radio-Loud and Radio-Quiet Gamma-Ray Pulsars from the Galaxy and the Gould Belt -- Gamma-Ray Emission from Pulsar Outer Magnetospheres -- Pulsar Wind Nebulae in EGRET Error Boxes -- Pulsar Radio and Gamma-Ray Emission -- Unidentified ?-Ray Sources off the Galactic Plane as Low-Mass Microquasars? -- On the Nature of the Variable Gamma-Ray Sources at Low Galactic Latitudes -- Spectral Properties of Black Holes in Gamma Rays -- Towards a Population of HMXB/NS Microquasars as Counterparts of Low-Latitude Unidentified EGRET Sources -- The Large-Scale, Decelerating X-Ray Jets from the Microquasar XTE J1550—564: Evidence for External Shocks Caused by the Jet-Ism Interaction? -- Gamma-Ray Emission from Be/X-Ray Binaries -- Low-Mass Quark Stars -- The Spiral ARM Connection of EGRET Unidentified Sources -- Cosmic Ray Acceleration Inside Molecular Clouds -- Methanol Masers as Precursors of Gamma-Ray Sources -- Identifying Variable ?-Ray Sources Through Radio Observations -- Revealing the Nature of the Obscured High Mass X-Ray Binary IGR J16318-4848 -- Status and First Results of the Magic Telescope -- The Neutrino Telescope Antares -- Identification of Shocks in the Spectra from Black Holes -- An Overview of the Veritas Prototype Telescope and Camera -- Comptel Constraints on Unidentified EGRET Sources -- On the Multiplicity of the O-Star Cyg OB2 #8A and its Contribution to the ?-Ray Source 3EG J2033+4118 -- Do the Unidentified EGRET Sources Trace Annihilating Dark Matter in the Local Group? -- Coherent Synchrotron Radiation of Gamma-Ray Bursts -- Constraints on Extra-Dimensions and Variable Constants from Cosmological Gamma-Ray Bursts -- Search for TeV Gamma-Rays from 3EG J1234-1318 with the CANGAROO-II Telescope -- Multiwavelength Study of Two Unidentified ?-Ray Sources -- A New TeV Source Confirmed in Whipple Archival Data: TeV J2032+41 -- The Prompt Ultraviolet/Soft X-Ray Emission of GRBs -- Periodicity Search in the X-Ray Data of RX J0007.0+7302 -- The Klein—Nishina Effects in Blazar Jets -- Detectivity of Unidentified EGRET Sources as Gamma-Ray Pulsars with the Magic Telescope -- On the Nature of the Unidentified X-Ray/?-Ray Sources IGR J18027-1455 and IGR J21247+5058 -- Status of the Connection between Unidentified EGRET Sources and Supernova Remnants: The Case of CTA 1 -- Spectral Constraints for Millisecond Pulsars Due to General Relativistic Frame Dragging -- A Multiwavelength Investigation of Unidentified EGRET Sources -- X-Ray Lines in Gamma-Ray Bursts and Cerenkov Line Mechanism -- Line Emission from Conical Jets Around Rotating Black Holes -- A Survey of Unidentified EGRET Sources at TeV Energies.Nearly one half of the point-like gamma-ray sources detected by EGRET instrument of the late Compton satellite are still defeating our attempts at identifying them. To establish the origin and nature of these enigmatic sources has become a major problem of current high-energy astrophysics. The second workshop on Multiwavelength Approach to Unidentified Gamma-ray Sources intends to shed new and fresh light on the problem of the nature of these mysterious sources and the objects behind them. The proceedings contain 46 contributed papers in this subject, which cover theoretical models on gamma-ray sources as well as the best multiwavelength strategies for the identification of the promising candidates. The topics of this conference also include energetic phenomena ocurring both in galactic and extragalactic scenarios, phenomena that might lead to the appearance of what we have called high-energy unidentified sources. The book will be of interest for all active researchers in the high-energy astrophysics and related research areas as well as for scientists and graduate students interested in understanding the recent progress in this field.