The term Environment etymologically means Surroundings. Thus environment is a complex of so many things (light, temperature, soil, water etc) which surround an organism. Any external force, substance or condition, which surrounds and affects the life of an organism in any way, becomes a factor of its environment. These factors have been variously called as environmental factors, ecological factors or simply factors and may be living (biotic) as well as non-living (abiotic). The sum of all these living and non-living factors makes the environment of an organism. The place, where an organism lives - habitat, indeed presents a particular set of environmental conditions - the environmental complex.

Various ecological factors of the environmental complex have been grouped and discussed in different ways:-

1. Direct Factors: These are light, temperature, humidity of air, soil, air, soil water, soil nutrients etc
2. Indirect Factors: These include soil structure, soil organisms, altitude, wind , slopes etc.
According to Oosting (1948), the environment is complex of variable factors or causes, which includes (i) substances (soil, water), (ii) conditions (temperature, light), (iii) forces (wind, gravity), (iv) organisms (plants, animals), and (v) time. Mishra and Puri (1959) preferrred to discuss the environment of plants as (i) Environment of roots (geogology and soil) and (ii) Environment of shoots (Climate, i.e temperature, light, water, wind etc and biotic factors)

Daubenmire (1959) classified the factors into seven coordinate headings as:

i) Soil ii) Water iii) Temperature  iv) Light  v) Atmosphere vi) Fire and vii) Biotic factor.
Most of the ecologists, however, prefer to recognise four categories of ecological factors, which are as follows:

1. Climatic or Aerial factors. These include:-
a)   Light
b)  Temperature of air (atmospheric temperature)
c)   Rainfall (precipitation)
d)   Humidity of air
e)   Atmosphere (gases and wind)

2. Topographic or Physiographic factors:-
These are factors related with physical geography of earth and include -
a)  Altitude
b)  Direction of mountain chains and valleys
c)  Steepness and exposure of slopes etc.

3. Edaphic Factors:- These deal with the formation of soil, its physical and chemical properties and details of related aspects.

4. Biotic Factors:- These are all kinds of intereactions between deifferent forms of life, i.e plants, animals, microorganisms etc 

Climate of any region is chiefly determined by such metereological influences as relative humidity of air, temperature, wind pressures and evaporation rates. Climatic factors characterise, in general a particular region. These factors, concerned mainly with the aerial environment of organisms, include light, temperature of air, precipitation (rainfall) and gaseous components of atmosphere including wind.

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