diff --git a/wake_t/beamline_elements/field_quadrupole.py b/wake_t/beamline_elements/field_quadrupole.py
index 8363e3f..345f828 100755
--- a/wake_t/beamline_elements/field_quadrupole.py
+++ b/wake_t/beamline_elements/field_quadrupole.py
@@ -18,8 +18,8 @@ class FieldQuadrupole(FieldElement):
         Length of the quadrupole lens in :math:`m`.
     foc_strength : float
         Focusing strength of the quadrupole in :math:`T/m`. Defined so
-        that a positive value is focusing for electrons in the :math:`y`
-        plane and defocusing in the :math:`x` plane.
+        that a positive value is focusing for electrons in the :math:`x`
+        plane and defocusing in the :math:`y` plane.
     dt_bunch : float, str, or list of float and str
         The time step for evolving the particle bunches. If ``'auto'``, it will
         be automatically set to :math:`dt = T/(10*2*pi)`, where T is the
diff --git a/wake_t/physics_models/em_fields/quadrupole.py b/wake_t/physics_models/em_fields/quadrupole.py
index 9f4960a..e4e3109 100644
--- a/wake_t/physics_models/em_fields/quadrupole.py
+++ b/wake_t/physics_models/em_fields/quadrupole.py
@@ -24,12 +24,12 @@ class QuadrupoleField(AnalyticalField):
 
     In Cartesian coordinates, the field is given by:
     ```
-        b_x = k * y
-        b_y = k * x
+        b_x = - k * y
+        b_y = - k * x
     ```
 
-    When `k > 0`, it corresponds to focussing electrons in the `y` direction
-    and defocussing in `x`. When `k < 0`, the result is the opposite.
+    When `k > 0`, it corresponds to focussing electrons in the `x` direction
+    and defocussing in `y`. When `k < 0`, the result is the opposite.
 
     Parameters
     ----------