There are 154 Shakespearean sonnets. They were not written as a coherent narrative but rather as individual poems, and thus, although there are certain themes that recur across several individual sonnets, there is not the sort of thematic unity one would find in a sonnet sequence intended as an organic whole.
The sonnet as a form, especially as developed by Petrarch, was often associated with the theme of love. Shakespeare is no exception to this, and the majority of the sonnets have love as a theme. This theme can be handled in many ways. Some of the sonnets praise the beloved directly and others indirectly. Some suggest that love can bring joy even when the narrator is surrounded by misfortune. Others emphasize that true love endures through age and involves a deep spiritual connection rather than just superficial physical attraction.
The love poems are mainly addressed to a young man but some are also addressed to a woman. They include themes of jealousy, unrequited love, and requited love. Some of the poems also address the nature of time and human mortality.
The themes of Shakespeare’s Sonnets are about love; they appear to be dedicated to a handsome boy and a rival poet together with a mysterious and aloof "dark" lady that they both love . They are divided into three groups:
o Sonnets 1 to 126 are addressed to or concern a young man
o Sonnets 127-152 are addressed to or concern a dark lady
o Sonnets 153-154 are free adaptations of two classical Greek poems
Well there are so many individual themes within each sonnet, but if you are looking for an overall theme, it would definintly be love--be it falling in or out of love (like the first 17 sonnets) or unrequited love (like sonnet's 127-154). One common theme that all of the Sonnets address is love.
If you try to look at the general context of Shakespeare's sonnets, you would therefore conclude that majority of his sonnets speak of love and admiration for a certain dark lady, his undying friendship for a young man and the rest where adaptation of greek classical forms.