diff --git a/dp_creator_ii/app/analysis_panel.py b/dp_creator_ii/app/analysis_panel.py
index fce6df6..ab17b60 100644
--- a/dp_creator_ii/app/analysis_panel.py
+++ b/dp_creator_ii/app/analysis_panel.py
@@ -28,7 +28,7 @@ def analysis_ui():
         log_slider("log_epsilon_slider", 0.1, 10.0),
         ui.output_text("epsilon"),
         output_code_sample("Privacy Loss", "privacy_loss_python"),
-        ui.input_action_button("go_to_results", "Download results"),
+        ui.output_ui("download_results_button_ui"),
         value="analysis_panel",
     )
 
@@ -41,6 +41,10 @@ def analysis_server(
     contributions=None,
     is_demo=None,
 ):  # pragma: no cover
+    @reactive.calc
+    def button_enabled():
+        column_ids_selected = input.columns_checkbox_group()
+        return len(column_ids_selected) > 0
 
     weights = reactive.value({})
 
@@ -67,9 +71,9 @@ def _update_checkbox_group():
 
     @reactive.effect
     @reactive.event(input.columns_checkbox_group)
-    def _update_weights():
-        column_ids_to_keep = input.columns_checkbox_group()
-        clear_column_weights(column_ids_to_keep)
+    def _on_column_set_change():
+        column_ids_selected = input.columns_checkbox_group()
+        clear_column_weights(column_ids_selected)
 
     @render.ui
     def columns_ui():
@@ -115,3 +119,16 @@ def privacy_loss_python():
     @reactive.event(input.go_to_results)
     def go_to_results():
         ui.update_navs("top_level_nav", selected="results_panel")
+
+    @render.ui
+    def download_results_button_ui():
+        button = ui.input_action_button(
+            "go_to_results", "Download results", disabled=not button_enabled()
+        )
+
+        if button_enabled():
+            return button
+        return [
+            button,
+            "Select one or more columns before proceeding.",
+        ]
diff --git a/dp_creator_ii/app/dataset_panel.py b/dp_creator_ii/app/dataset_panel.py
index 30922bb..2be9b67 100644
--- a/dp_creator_ii/app/dataset_panel.py
+++ b/dp_creator_ii/app/dataset_panel.py
@@ -31,10 +31,11 @@ def dataset_ui():
             "contributions",
             ["Contributions", ui.output_ui("contributions_demo_tooltip_ui")],
             cli_info.contributions,
+            min=1,
         ),
         ui.output_ui("python_tooltip_ui"),
         output_code_sample("Unit of Privacy", "unit_of_privacy_python"),
-        ui.input_action_button("go_to_analysis", "Define analysis"),
+        ui.output_ui("define_analysis_button_ui"),
         value="dataset_panel",
     )
 
@@ -52,6 +53,14 @@ def _on_csv_path_change():
     def _on_contributions_change():
         contributions.set(input.contributions())
 
+    @reactive.calc
+    def button_enabled():
+        contributions_is_set = input.contributions() is not None
+        csv_path_is_set = (
+            input.csv_path() is not None and len(input.csv_path()) > 0
+        ) or is_demo
+        return contributions_is_set and csv_path_is_set
+
     @render.ui
     def choose_csv_demo_tooltip_ui():
         return demo_tooltip(
@@ -78,6 +87,18 @@ def python_tooltip_ui():
             "for the entire calculation.",
         )
 
+    @render.ui
+    def define_analysis_button_ui():
+        button = ui.input_action_button(
+            "go_to_analysis", "Define analysis", disabled=not button_enabled()
+        )
+        if button_enabled():
+            return button
+        return [
+            button,
+            "Choose CSV and Contributions before proceeding.",
+        ]
+
     @render.code
     def unit_of_privacy_python():
         return make_privacy_unit_block(contributions())
diff --git a/tests/test_app.py b/tests/test_app.py
index 9a75dd1..624b276 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -47,12 +47,17 @@ def expect_no_error():
     expect_visible("dp.unit_of(contributions=42)")
     expect_no_error()
 
+    # Button disabled until upload:
+    define_analysis_button = page.get_by_role("button", name="Define analysis")
+    assert define_analysis_button.is_disabled()
+
+    # Now upload:
     csv_path = Path(__file__).parent / "fixtures" / "fake.csv"
     page.get_by_label("Choose CSV file").set_input_files(csv_path.resolve())
     expect_no_error()
 
     # -- Define analysis --
-    page.get_by_role("button", name="Define analysis").click()
+    define_analysis_button.click()
     expect_not_visible(pick_dataset_text)
     expect_visible(perform_analysis_text)
     expect_not_visible(download_results_text)
@@ -72,12 +77,18 @@ def expect_no_error():
     expect_visible("Epsilon: 0.316")
     page.locator(".irs-bar").click()
     expect_visible("Epsilon: 0.158")
+
+    # Button disabled until column selected:
+    download_results_button = page.get_by_role("button", name="Download results")
+    assert download_results_button.is_disabled()
+
     # Set column details:
     page.get_by_label("grade").check()
     page.get_by_label("Min").click()
     page.get_by_label("Min").fill("0")
     # TODO: All these recalculations cause timeouts:
     # It is still rerendering the graph after hitting "Download results".
+    # https://github.com/opendp/dp-creator-ii/issues/116
     # page.get_by_label("Max").click()
     # page.get_by_label("Max").fill("100")
     # page.get_by_label("Bins").click()
@@ -86,7 +97,7 @@ def expect_no_error():
     expect_no_error()
 
     # -- Download results --
-    page.get_by_role("button", name="Download results").click()
+    download_results_button.click()
     expect_not_visible(pick_dataset_text)
     expect_not_visible(perform_analysis_text)
     expect_visible(download_results_text)