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In alkenes we can find position isomerism, chain isomerism and geometric isomerism.

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In alkenes with a carbon chain composed of 4 or more carbon atoms we can have position isomerism: in fact, the position of double bond can vary. When naming alkenes we have to specify the position of the double bond along the carbon chain using a number as prefix. This number indicates the position of the carbon involved in the double bond that came first in the order of the carbon chain.

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In alkenes we can find chain isomers because of the possibility to find alkenes with the same molecular formula but different lenght of the carbon chain. When naming alkenes we have to individuate the longest carbon chain and numerate it in order to give to the atoms involved in the double bond the smallest number possible.

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In alkenes there is not free rotation in the carbon atoms due to the presence of the double bond. When both the carbon atoms are linked to two atomic groups or atoms different from the hydrogen, we can have geometric isomerism. the two substinuents can be found in the same part relative to the double bond or in differents parts.
In the first case tha name of the molecule is preceded by the prefix "cis-", in the second case by the prefix "trans-".
geometric isomers aren't spontaniusly interconvertible.