Solidarity is unity (as of a group or class) that produces or is based on community of interests, objectives, and standards. It refers to the ties in a society that bind people together as one. The term is generally employed in sociology and the other social sciences.
What forms the basis of solidarity varies between societies. In simple societies it may be mainly based around kinship and shared values. In more complex societies there are various theories as to what contributes to a sense of social solidarity.
- "Thus, a group's solidarity is a function of two independent factors: first, the extensiveness of its corporate obligations, and, second, the degree to which individual members actually comply with these obligations. Together, these provide the defining elements of solidarity. The greater the average proportion of each member's private resources contributed to collective ends, the greater the solidarity of the group." - Michael Hechter 
- International solidarity is "not an act of charity but an act of unity between allies fighting on different terrains toward the same objectives." - Samora Machel
- "Unlike solidarity, which is horizontal and takes place between equals, charity is top-down, humiliating those who receive it and never challenging the implicit power relations." - Eduardo Galeano
- "Solidarity is not a matter of altruism. Solidarity comes from the inability to tolerate the affront to our own integrity of passive or active collaboration in the oppression of others, and from the deep recognition of our most expansive self-interest. From the recognition that, like it or not, our liberation is bound up with that of every other being on the planet, and that politically, spiritually, in our heart of hearts we know anything else is unaffordable." - Aurora Levins Morales
- "Solidarity does not assume that our struggles are the same struggles, or that our pain is the same pain, or that our hope is for the same future. Solidarity involves commitment, and work, as well as the recognition that even if we do not have the same feelings, or the same lives, or the same bodies, we do live on common ground." - Sara Ahmed
- "No man is an island, entire of itself; every man is a piece of the continent, a part of the main. If a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as if a manor of thy friend's or of thine own were: any man's death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bells tolls; it tolls for thee. Neither can we call this a begging of misery, or a borrowing of misery, as though we were not miserable enough of ourselves, but must fetch in more from the next house, in taking upon us the misery of our neighbours. Truly it were an excusable covetousness if we did, for affliction is a treasure, and scarce any man hath enough of it. No man hath affliction enough that is not matured and ripened by and made fit for God by that affliction. If a man carry treasure in bullion, or in a wedge of gold, and have none coined into current money, his treasure will not defray him as he travels. Tribulation is treasure in the nature of it, but it is not current money in the use of it, except we get nearer and nearer our home, heaven, by it. Another man may be sick too, and sick to death, and this affliction may lie in his bowels, as gold in a mine, and be of no use to him; but this bell, that tells me of his affliction, digs out and applies that gold to me: if by this consideration of another's danger I take mine own into contemplation, and so secure myself, by making my recourse to my God, who is our only security." - John Donne, Meditation XVII