The Four Noble Truths
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Truth about the existence of suffering
Truth about the causes of suffering
Truth about the existence of happiness
Truth about the path to follow

The Eightfold Path

The Middle Way is also called the Noble Eightfold Path, because it comprises eight divisions, all of which must be developed simultaneously.
- right understanding
- right thought
- right speech
- right action
- right livelihood
- right effort
- right attention
- right concentration
These eight branches enable the development and perfection of the three main elements of Buddhist training and discipline:
- ethical conduct (shila)
- mental discipline (samadhi)
- wisdom (prajna)

Impermanence

A fundamental principle of Buddhism, it applies to all things which, in their general and constant correlations, are in perpetual transitions of state.
This changeable, transitory character of all existence is called "impermanence". It is a universal reality, present in the world, in beings and in all situations. Impermanence makes birth, death, life and knowledge possible; it is also what causes us to die.

Interdependence

The Buddha's teaching, the dharma, teaches us that everything is interdependent: what we are and our world, everything that exists and everything that is known. There is nothing, no experience or knowledge, that is not dependent on something else!
Moreover, what we are as individuals is also seen by Dharma as a set of interacting elements. At a first, commonly accepted level, this is a quasi-scientific notion: that of a world as a network of interconnections, of cause-and-effect relationships.
The notion of interdependence thus understood goes hand in hand with that of impermanence.

Emptiness

Śūnyatā, Sanskrit term, in devanāgarī शून्यता; in Pali suññata, in Chinese kōng 空, designates in Buddhism the emptiness or ainsity (tathatā) of beings and things, their absence of being in itself, in other words the non-existence of any essence, any fixed and unchanging character.
It applies to things as well as to thoughts and states of mind.
According to Buddhism, everything is in essence emptiness (śūnyatā), both samsâra and nirvâna. Śūnyatā does not mean "emptiness". It's a very difficult word to understand and define. It is with reservation that I translate it as "emptiness". The best definition, in my opinion, is "interdependence", which means that everything depends on others to exist. [...] Everything is by nature interdependent, and therefore void of its own existence.
Emptiness does not empty things of their content; it is their true nature

Philippe Cornu, quoting the Madhyamika philosopher Nāgārjuna,

Encyclopedic Dictionary of Buddhism