1 Introduction.- 2 Temperature.- 3 Water Vapor and Other Gases.- 4 Liquid Water in Organisms and their Environment.- 5 Wind.- 6 Heat and Mass Transport.- 7 Conductances for Heat and Mass Transfer.- 8 Heat Flow in the Soil.- 9 Water Flow in Soil.- 10 Radiation Basics.- 11 Radiation Fluxes in Natural Environments.- 12 Animals and their Environment.- 13 Humans and their Environment.- 14 Plants and Plant Communities.- 15 The Light Environment of Plant Canopies.