Fog and Boundary Layer Clouds: Introduction -- Obituary -- Fog Research: A Review of Past Achievements and Future Perspectives -- Microphysical Observations and Mesoscale Model Simulation of a Warm Fog Case during FRAM Project -- Dynamical Nighttime Fog/Low Stratus Detection Based on Meteosat SEVIRI Data: A Feasibility Study -- Inferring Low Cloud Base Heights at Night for Aviation Using Satellite Infrared and Surface Temperature Data -- Analysis of Fog Probability from a Combination of Satellite and Ground Observation Data -- The Impact of Vertical Resolution in the Explicit Numerical Forecasting of Radiation Fog: A Case Study -- A One-dimensional Ensemble Forecast and Assimilation System for Fog Prediction -- Quality Assessment of the Cobel-Isba Numerical Forecast System of Fog and Low Clouds -- Seasonal Sensitivity on COBEL-ISBA Local Forecast System for Fog and Low Clouds -- Can Sea Fog be Inferred from Operational GEM Forecast Fields? -- Implementation of a Single-Column Model for Fog and Low Cloud Forecasting at Central-Spanish Airports -- Synoptic Classification and Establishment of Analogues with Artificial Neural Networks -- Probabilistic Visibility Forecasting Using Neural Networks -- Climatological Tools for Low Visibility Forecasting -- Marine Layer Stratus Study. The e?ect of fog on human life was recognized in the early ages of mankind but its impact has signi?cantly increased during recent decades due to increasing air, marine, and road tra?c. In fact, the ?nancial and human losses related to fog and low visibility became comparable to the losses from other weather events, e.g., tornadoes or, in some situations, even hurricanes. The purpose of this review is to summarize the earlier works on fog and to lay a basis for the articles presented in this special issue and outline perspectives for future fog research. The earliest works on fog can be traced back to Aristotle's Meteorologica (284- 322 B.C.). These were extensively referenced by NEUMANN (1989) in his study of early works on fog and weather. This paragraph is mainly based on his detailed work. In the English translation by H.D.P. Lee (1962, ARISTOTLE), a statement is given on the relationship between fog and good weather. Also, NEUMANN (1989) relates a poem by ARATUS (315-240 B.C.), which was referred to as Prognostication Through Weather Signs, in an English translation by G.R. Mair (ARATUS, 1921).