diff --git a/include/interpol2.h b/include/interpol2.h
new file mode 100644
index 0000000000000000000000000000000000000000..283035d293a23846a75f0f69ff8506c64143502f
--- /dev/null
+++ b/include/interpol2.h
@@ -0,0 +1,65 @@
+/** @file interpol2.h
+ * @brief Header file for interpol2.c.
+ */
+#ifndef _INTERPOL2_H_
+
+/* We will certainly never use a 16th order scheme,
+ * but in case we do, remember to change it here
+ */
+#define MAX_ORDER 16
+
+#define MAX_INTERPOL_METHODS 9
+
+typedef struct interpol_t interpol_t;
+typedef struct interpol_method_t interpol_method_t;
+
+struct interpol_t
+{
+  double *coeffs;
+  double *stencil;
+
+  /* The separation between stencil points. */
+  double Lr, Lz;
+
+  /* The interpolation method to use. */
+  interpol_method_t *method;
+
+  /* Origin of the interpolation polynomial, which is thus written in
+     powers of (r - r0) and (z - z0). */
+  double r0, z0;
+};
+
+struct interpol_method_t
+{
+  double *matrix;
+
+  /* p is the order of the polynomial plus one.
+   * q is the number of stencil points in one direction (the total
+   * number is, of course, q^2. */
+  int p, q;
+
+  /* Location of the origin with respect to the stencil in units of L. */
+  int ir0, iz0;
+
+  int masses;
+
+  void (*set_coeffs) (interpol_t *this);
+  double (*apply) (interpol_t *this, double r, double z);
+};
+
+extern interpol_method_t interpol_zero;
+extern interpol_method_t interpol_wackers;
+extern interpol_method_t interpol_luque;
+extern interpol_method_t interpol_quadratic;
+extern interpol_method_t interpol_bilin;
+extern interpol_method_t interpol_quadlog;
+extern interpol_method_t interpol_zero_masses;
+extern interpol_method_t interpol_wackers_masses;
+extern interpol_method_t interpol_luque_masses;
+extern interpol_method_t interpol_quadratic_masses;
+extern interpol_method_t interpol_bilin_masses;
+
+extern interpol_method_t *interpol_methods_index[MAX_INTERPOL_METHODS];
+
+#define _INTERPOL2_H_
+#endif