diff --git a/networks.rkt b/networks.rkt
index 7548d86..590df13 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -13,6 +13,8 @@
 (require "utils.rkt" graph)
 
 (provide
+ ;; Structures
+ (struct-out dynamics)
  ;; Functions
  (contract-out [update (-> network? state? (listof variable?) state?)]
                [make-state (-> (listof (cons/c symbol? any/c)) state?)]
@@ -33,7 +35,8 @@
  (contract-out [variable? (-> any/c boolean?)]
                [state? (-> any/c boolean?)]
                [update-function-form? (-> any/c boolean?)]
-               [network-form? (-> any/c boolean?)])
+               [network-form? (-> any/c boolean?)]
+               [mode? (-> any/c boolean?)])
  ;; Contracts
  (contract-out [state/c contract?]
                [network/c contract?]
@@ -237,3 +240,17 @@
 (define (build-boolean-signed-interaction-graph network-form)
   (build-signed-interaction-graph network-form
                                   (make-boolean-domains (hash-keys network-form))))
+
+
+;;; ====================
+;;; Dynamics of networks
+;;; ====================
+
+;;; This section contains definitions for building and analysing the
+;;; dynamics of networks.
+
+;;; A mode is a set of sets of variables.
+(define mode? (set/c (set/c variable?)))
+
+;;; A network dynamics is a network plus a mode.
+(struct dynamics (network mode))