Do hadrons only interact via strong interaction? According to my revision guide baryon and mesons always interact via the strong interaction. 
Does this hold for baryon-baryon interactions? meson-meson?
Thanks
 A: Quarks, the constituents of hadrons/mesons, interact via the strong, weak and electromagnetic force. So hadrons/mesons do interact via all this forces, too. Even if the total net-carge is zero. Take for instance the neutron, which has zero electric charge. Still it has a magnetic moment which gives rise to electromagnetic interactions. It can also decay via a weak process, which is commonly known as beta-radiation.
A: Charged hadrons, and neutral hadrons with nonzero magnetic moment, interact electromagnetically. A spinless, neutral hadron would not couple to the electromagnetic field at tree level, but the most obvious example of such a particle is the $\pi^0$, which decays electromagnetically to two photons.
All particles with flavor participate in the weak interaction. You mostly hear about this in terms of decays, because for ordinary interaction energies the weak interaction is too feeble to contribute much to the dynamics. You can consider the weak interaction between strongly- or electromagnetically-interacting particles as a Yukawa-type force,
$$
V \propto \frac{e^{-r/r_0}}{r},
$$
where the length scale is set by the mass of the weak boson, $r_0 \approx (\hbar c) / (m_Wc^2)$. 
However, the weak interaction has a different set of symmetries than
the strong and electromagnetic forces. Specifically, the weak
interaction is broken under parity
transformations,
while the strong and E&M transitions are not. You can therefore peer
down into the short-distance physics of low-energy interactions by
looking for parity-violating observables.  The most common  method is
to look for an asymmetry in a scalar quantity, like reaction rate,
that depends on the angle between a spin and a momentum,
$\vec\sigma\cdot\vec p$.
The purely hardronic weak interaction (by which I mean, without any leptonic decays involved) is a hard thing to suss out theoretically,
because the strong force is both (a) strong, and (b) complicated.
In many-body systems, you may have opposite-parity excited states
which happen to be nearly degenerate in energy and are mixed by the
weak interaction.
The largest known enhancement of this type, to my knowledge, occurs in
some of the excited states probed by
neutron capture on lanthanum: there is a correlation between the
incoming neutron's spin $\vec\sigma_\text{n}$ and the outgoing photon's
direction $\vec k_\gamma$ that turns out to be a 10% asymmetry.
But lanthanum is an enormously complicated nucleus.
In neutron capture on hydrogen the same asymmetry is about ten parts
per billion.
So, while hadrons always interact via the strong interaction, they
certainly do not only interact via the strong interaction.
