OVERVIEW OF PHOTOMORPHOGENESIS -- HISTORICAL OVERVIEW -- PHYSIOLOGICAL BASIS OF PHOTOMORPHOGENESIS -- HISTORICAL OVERVIEW OF MOLECULAR BIOLOGY AND GENETICS IN PHOTOMORPHOGENESIS -- GENETIC BASIS AND MOLECULAR MECHANISMS OF SIGNAL TRANSDUCTION FOR PHOTOMORPHOGENESIS -- THE PHYTOCHROME -- THE PHYTOCHROME CHROMOPHORE -- STRUCTURE, FUNCTION, AND EVOLUTION OF MICROBIAL PHYTOCHROMES -- PHYTOCHROME GENES IN HIGHER PLANTS: STRUCTURE,EXPRESSION, AND EVOLUTION -- PHYTOCHROME DEGRADATION AND DARK REVERSION -- INTRACELLULAR LOCALIZATION OF PHYTOCHROMES -- BLUE-LIGHT AND UV-RECEPTORS -- BLUE/UV-A RECEPTORS: HISTORICAL OVERVIEW -- CRYPTOCHROMES -- PHOTOTROPINS -- BLUE LIGHT PHOTORECEPTORS -BEYOND PHOTOTROPINS AND CRYPTOCHROMES -- UV-B PERCEPTION AND SIGNALLING IN HIGHER PLANTS -- SIGNAL TRANSDUCTION IN BLUE LIGHT-MEDIATED RESPONSES -- SIGNAL TRANSDUCTION IN PHOTOMORPHOGENESIS -- GENERAL INTRODUCTION -- PHYTOCHROME SIGNAL TRANSDUCTION NETWORK -- THE FUNCTION OF THE COP/DET/FUS PROTEINS IN CONTROLLING PHOTOMORPHOGENESIS: A ROLE FOR REGULATED PROTEOLYSIS -- BIOCHEMICAL AND MOLECULAR ANALYSIS OF SIGNALLING COMPONENTS -- THE PHOTORECEPTOR INTERACTION NETWORK -- INTERACTION OF LIGHT AND HORMONE SIGNALLING TO MEDIATE PHOTOMORPHOGENESIS -- SELECTED TOPICS -- THE ROLES OF PHYTOCHROMES IN ADULT PLANTS -- A ROLE FOR CHLOROPHYLL PRECURSORS IN PLASTID-TO-NUCLEUS SIGNALING -- PHOTOMORPHOGENESIS OF FERNS -- PHOTOMORPHOGENESIS OF MOSSES -- CIRCADIAN REGULATION OF PHOTOMORPHOGENESIS -- THE MOLECULAR GENETICS OF PHOTO PERIODIC RESPONSES:COMPARISONS BETWEEN LONG-DAY AND SHORT-DAY SPECIES -- COMMERCIAL APPLICATIONS OF PHOTOMORPHOGENESIS RESEARCH -- PHOTOMORPHOGENESIS - WHERE NOW?. Plants as sessile organisms have evolved fascinating capacities to adapt to changes in their natural environment. Arguably, light is by far the most important and variable environmental factor. The quality, quantity, direction and duration of light is monitored by a series of photoreceptors covering spectral information from UVB to near infrared. The response of the plants to light is called photomorphogenesis and it is regulated by the concerted action of photoreceptors. The combined techniques of action spectroscopy and biochemistry allowed one of the important photoreceptors - phytochrome - to be identified in the middle of the last century. An enormous number of physiological studies published in the last century describe the properties of phytochrome and its function and also the physiology of blue and UV-B photoreceptors, unidentified at the time. This knowledge was summarized in the advanced textbook "Photomorphogenesis in Plants" (Kendrick and Kronenberg, eds., 1986, 1994). With the advent of molecular biology, genetics and new molecular, cellular techniques, our knowledge in the field of photomorphogenesis has dramatically increased over the last 15 years.